Document text
.BORATORY AND FIELD
MANUAL OF BOTANY
z
Py-
BY
JOSEPH Y. BERGEN, A.M.
_ Aurion oF “ ELEMENTS OF BOTANY,” * FounDaTtons OF BOTANY,”
“ PRIMER OF DARWINISM,” ETO.
BRADLEY M. DAVIS, PED.
— UNIVERSITY OF CHICAGO
`
COPYRIGHT, 1907, BY EN
JOSEPH Y. BERGEN AND BRADLEY M. DAVIS a
ALL RIGHTS RESERVED
PREFACE
This manual offers material for much more than a year’s
laboratory work. This is made necessary by the fact that in-
structors differ widely in their views as to what matter should
be presented in an introductory course under the variety of
conditions obtaining where botany is taught. A course must
necessarily be framed selectively, and the chief alternatives are
discussed in the opening paragraphs of the Introduction.
The authors fully recognize the fact that no set of directions
of only moderate fullness can tell the student all that he needs
to know about choice of material, apparatus, and manipulation.
It is assumed that much is left to be explained by the instructor,
and constant mention is made of general and special laboratory
guides which may be consulted for needed details.
The student in the laboratory is not to consider himself as
merely the corroborator of facts already ascertained: he is to
interrogate mainly not the instructor, not the manual, but the
plant itself. The directions here given are, therefore, for the
most part suggestions on methods of procedure and indications
as to the plants or parts of plants in which to look for desired
information.
Since the amount of ground that can be covered by labora-
tory divisions varies so largely with many circumstances, it has
seemed desirable to designate two courses, a briefer and a fuller
one. The matter which may be omitted from the latter to frame
the shorter course is printed in smaller type and consists in the
: main of rather more difficult or detailed studies than those which
appear in the larger type. In a general way the order of treat-
ment follows that of the authors’ Principles of Botany, but the
60622
iv : PREFACE
shorter course does not cover many more topics than are dealt
with in Bergen’s Klements or Foundations of Botany, and may be
used with either of those books.
Part I consists mainly of studies on the gross anatomy and
the histology of seed plants, together with a set of separately —
- numbered experiments to illustrate some of the main principles
of plant physiology.
Part II deals with type studies of spore plants, outlining the
` -evolution and classification of the plant kingdom. Here will also
be found studies on the gametophyte phases and the life histories
of seed plants to show their relationships to the spore plants.
Part II is introduced by outlines on the plant cell to illustrate
the chief principles of growth and reproduction.
Part III is concerned with a series of laboratory and field
studies which may serve to offer at least an outline for the
treatment of ecology as a scientific subject. Profound ecological
studies demand far more knowledge of taxonomy, plant phys-
iology, meteorology, the physics and chemistry of soils, and
kindred subjects than can be required of beginners in botany.
However, the authors believe that it is quite possible to illustrate,
even to beginners, something of the kind of quantitative discus-
sion of variations in environment and the responses of plants
to changed conditions, which must distinguish the ecology of
the future.
Hearty acknowledgments for valuable suggestions are due to
A. T. Bell, F. E. Clements, W. N. Clute, W. F. Ganong, B. Gruen-
berg, Miss Lillian J. MacRae, G. J. Peirce, and R. B. Wylie, who
have wholly or in part read the manuscript or the E
CAMBRIDGE, March, 1907
CONTENTS
F PAGE
INTRODUCTION . : . : à . sed Ml
LABORATORY METHODS AND ) EQUIPMENT ; : : poet:
PART I—STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
Introductory Study of a Seed Plant and its Organs ; , . 15
The Seed and its Germination z 5 : ; ; : T
Storage of Food in the Seed . . : ; z om ra
Movements, Development, and Morphology of the Seeding ; ; a
Roots . : : 1 £29
Some Poeren of Cells and thou Tanen in the Root : : . 386
Stems. lal =! i A ; ; : : : E ait
Structure of ihe San ; : ; s A y 3 St!)
Work of the Stem . : : : : ; ‘ : : R . 45
Buds : i ; ; : ‘ . : 3 i : ; . 48
Leaves . ; é 5 : : : . bl
Leaf Arrangement with Raters i Light ; ; ; : ; . 68
Minute Structure and Functions of Leaves . ; ; ; F o
The Flower of the Higher Seed Plants . i F ; ` : . 64
Pollination and Fertilization . š : ; : à : : . 68
The Fruit A ` 5 A š f ; A ; ; i . 69
PART JI—TYPE STUDIES PRECEDED BY THE STUDY
OF THE PLANT CELL
The Plant Cell, its Structure and Reproduction . 3 f 3 a aie
The Flagellates, or Flagellata 3 4 À é k : : . 88
The Slime Molds, or Myxomycetes : ; ; : } t . 83
The Blue-Green Algæ, or Cyanophyceæ ; ; ‘ ; : . 84
The Green Algæ, or Chlorophycez : 3 : > p : Panel
The Brown Algze, or Pheophycee . à > : : : r eo
The Red Algze, or Rhodophycee . š ; é 5 č . 100
The Bacteria, or Schizomycetes . 5 4 : a 5 a . 102
The Yeasts, or Saccharomycetes . 3 ; : : : 5 . 105
The Alga-like Fungi, or Phycomycetes . 5 i é ; í = 107
My
vi CONTENTS
The Sac Fungi, or Ascomycetes
The Lichens
The Basidia Fungi, or Ranidiniyeotes
The Liverworts, or Hepatice .
The Mosses, or Musci
The Ferns, or Filicinez .
The Horsetails, or Equisetinez
The Club Mosses, or Lycopodinez
The Gymnosperms, or Gymnospermze
The Angiosperms, or Angiospermz
PART II — ECOLOGY
Parasitic and Carnivorous Plants
How Plants protect themselves from Anaad
Pollination of Flowers
How Plants are scattered and propag ated
Competition and Inyasion
Plant Successions
Ecological Classes . :
Plant Formations ; Zonation .
Study of Types of Seed Plants
BOTANICAL MICROTECHNIQUE
General Reagents employed in Temporary Preparations
Some Special Reagents for Microchemical Tests and PES P
rations
Killing and Fixing .
The Preservation of Material >
General Staining Methods
Mounting in Balsam and Glycerin
Imbedding in Paraffin
Sectioning
Staining on the Slide
CULTURE METHODS.
The Culture of Algæ
The Culture of Fungi ;
The Culture of Liverworts bad Mose ;
The Culture of Ferns
The Culture of Seed Plants
CONTENTS vii
MATERIAL, APPARATUS, AND SUPPLIES
PAGE
Lists of Preparations for the Microscope : 3 ; SPAN
Suggestions on Material for the Study of Plant Estola Payee : . 220
Apparatus for the Laboratory ; : : : : : ; . 222
Chemicals for the Laboratory : ` ; 3 5 . 224
Dealers in Material, Apparatus, and Bipplies: 7 . : 5 . 225
BIBLIOGRAPHY . ; : : : ` ; ; : <- 227
APPENDIX . : : : : à : ; : ; p . 233
GLOSSARY . ; ; ; ; ; ; ; : s : . 241
INDEX . : ; : i ; : ; : ; : ; . 255
LIST OF EXPERIMENTS
PAGE
I. Temperature and germination 5 : ; A : = lo:
II. Amount of water in seeds s : ; ; ` ; T20
Ill. Relation of air to germination : ‘ ; : : = 21
IV. Effect of germination on air . A : : A o all
V. Use of the pea cotyledons after em sated ; i eal
VI. Relation of food in seed to rate of growth . i : T22
VII. Occurrence of starch in seeds : 2 i : : . 24
VIII. Oil in flaxseed A ; : : 3 ; 3 : 5 25
IX. Proteids in seeds . : y é : A c ‘ 26
X. Plant foods in Brazil nuts . > . : ò F .. 26
XI. Cause of arch of hypocotyl . : i ; : ee
XII. Discrimination between root and bon : ; , . 28
XIII. Growing region of root . : ; : : ; = 28
XIV. Percentage of water in the plant ody È $ : ; . 33
XV. Water cultures ; ; : . 33
XVI. Root absorption with dunmmiahed areata a : . 34
XVII. Region of bending in the root : > : 5 3 . 85
XVIII. Pressure of root tip 3 5 ę s : . 0d
XIX. Cause of downward abe of oor ; ‘ ; : ae OG
XX. Osmosis . 5 ; ; : š : ; . 3
XXI. Osmosis of Begonia Wat £ i r 3 4 ; <8
XXII. Course of water in stems é ; i . 45
XXIII. Relation of loss of water to franos of entes ` ; . 46
XXIV. Use ofcork . ; ‘ A 5 3 r ` : hE
viil
ZLQ
XXVI.
XXVII.
XXVIII.
XXIX.
XXX.
XXXI.
XXXII.
XXXIII.
XXXIV.
XXXV.:
XXXVI.
XXXVII
XXXVIII.
XXXIX.
XL.
XLI.
XLII.
CONTENTS
PAGE
Reserve sugar in onion bulb 48
Proteids in onion bulb : 48
Cause of nocturnal position of leaves . 53
Values of illumination for leaf positions f 53
Adaptation of growing leaves to changed light relations 54
Heliotropic movements of English ivy 55
Oxygen making by plants 57
Starch in Tropwolum leaves 57
Consumption of starch in Tropæolum ee 58
Effect of sealing stomata on starch production 59
Effect of darkness on chlorophyll production 59
Transpiration : 60
Side of Ficus elastica leaf which hae 61
Relative transpiration of Hydrangea Hortensia and T
elastica 61
Passage of water N on to leaf 63
Rise of water in leaves : : “i308
Starch contents of leaves at various seasons -63
Production of pollen tubes . 68
~
er
LABORATORY AND FIELD
MANUAL- OF BOTANY
INTRODUCTION
It is intended that these laboratory outlines shall be found
adaptable to several methods of approach in framing a general
course in elementary botany.
First. By beginning with Part I the student may consider first
the more general features of the morphology of the seed plant
and the most important of its physiological activities. This
may then be followed by studies of a series of spore plants
(Part IT), to outline the chief steps in plant evolution. Such work
as is possible in plant ecology (Part III) is thus deferred to the
end of the course.
Second. By commencing with Part II the student will be
introduced at once to the principles of cell structure, growth, and
reproduction, and can then trace the evolution of the plant king-
dom. By this arrangement selections from Part I will follow the
studies of Part II, and Part III will receive attention last.
Third. Part I may be followed at once by Part III, and the
studies of Part II be used only to illustrate such types and topics
concerned with spore plants as may seem desirable.
Fourth. It is by no means necessary that the matter of Part I
be taken up in the order given. Instead of beginning with the
plant as a whole or with the seed, a course may be readily shaped
so as to commence with the fruit or with the leaf.
The planning of a course depends upon so many factors, such as
season, material, equipment, maturity of students, and the time
1
2 INTRODUCTION
at the disposal of the class, that it must vary greatly with the
different conditions. The authors, recognizing these difficulties,
have tried to present a flexible outline in a thoroughly practical
manual containing sufficient material to permit of a wide range
of choice. In general they believe that the best results will
be obtained, when a full year can be devoted to the subject, by
taking the matter in the order given in the first or second of
the alternatives presented above. If only a half year is avail-
able, the best course in their judgment is that indicated in the
third alternative.
For the guidance of any who may care for such suggestions the
authors have designated by double asterisks (**) those experiments
and studies which they consider to be the most valuable.
A brief discussion of laboratory methods and equipment is
presented immediately before the laboratory outlines and experi-
ments of Parts I, II, and III. It is hoped that the instructor may
find some helpful suggestions in this, and certain parts are
written expressly to aid the student to an understanding of the
spirit of laboratory work, methods of drawing, note taking, and
the care of instruments.
The essential methods of botanical microtechnique and the
preparation of the material are taken up after the laboratory out-
lines. This account has been introduced to assist the instructor
and the advanced student in the collection and preservation of
material and in the more detailed studies of plant histology and
cytology, which demand the preparation of microtome sections
and critical staining methods. The discussion does not attempt
to give such details covering special studies as may be found in
several more exhaustive treatises to which the reader will be
referred. It endeavors rather to outline standard methods of,
killing, fixing, preserving, cutting, and staining plant structures,
which cannot fail to give good results, with the reasons why
they have been selected. Some simple directions for the culture
of alge, fungi, moss protonema, fern prothallia, etc., follow the
account of microtechnique.
INTRODUCTION 3
A section entitled “ Material, Apparatus, and Supplies ” gives
lists of preparations for the microscope, favorable material for
histological work, apparatus and supplies, with the addresses of
dealers who furnish these to the trade.
The bibliography has been chosen with the purpose of present-
ing a group of books many of which are within the possibilities
even of a well-equipped school library, rather than a lengthy list
of detailed literature which is usually only handled by the spe-
cialist. These works are numbered and the references to them
throughout the manual will be by the author’s name and the
number. ;
An appendix with suggestions to instructors follows the bibliog-
raphy. This contains matter which it is not necessary for the
student to read in connection with his laboratory work, although
in many cases it may be of interest for him to do so. The ap-
pendix is really a collection of practical notes based on the
experience of the authors or gathered from conversations and
correspondence with many teachers. Indeed, it is a feature which
the authors have introduced in the hope that it may bring forth
other helpful and practical suggestions from those who use the
book, and correspondence upon this subject is cordially invited.
A glossary gives a selected list of botanical terms, including
the most important of those used in this manual and in the
authors’ Principles of Botany.
Only a few necessary abbreviations have been used, to econo-
mize space. As stated above, books listed in the bibliography
are referred to by the author’s name and number in the list.
Principles designates the Principles of Botany; App., the ap-
pendix; l.p., m.p., and h.p. refer to low power, medium power,
and high power of the compound microscope respectively; lens
means either hand lens or dissecting microscope as the case may
be; c.p. means chemically pure. The usual abbreviations for
the units of the metric system are frequently employed.
LABORATORY METHODS AND EQUIPMENT
THE LABORATORY AND ITS EQUIPMENT
The essentials of a laboratory are, of course, good light, con-
venient tables, and sufficient apparatus. While north light is
preferable, since its quality is more constant, east, west, or south
light can be perfectly regulated by translucent shades which may
be pulled up to any desired distance, and so temper direct sun-
light when necessary. Moreover, it is desirable that some win-
dows have the sun for part of the day, since aquaria and glass
eases for growing plants require some sunlight and may be placed
in such parts of the room. Excellent suggestions on the arrange-
ment of laboratory tables, lockers, glass growing case, sink, black-
board, etc., are given in Ganong, T, Chapter V, and in Lloyd, 8,
Chapter LX, books which should be read by every teacher of botany.
The equipment of a laboratory will depend largely upon the
nature of the work, whether very elementary or covering a strong
full course of a year or more, and also upon the attitude of the
instructor, who may emphasize especially either physiology or a
more detailed morphology. Physiology requires its own special
apparatus, and detailed morphology demands the equipment
necessary for imbedding, microtome section cutting, and staining.
Much of the work with this apparatus can best be conducted at
tables in the center or back of the laboratory, which will not
interfere with the tables for the more general class exercises. In
the choice of equipment and its storage the instructor is again
referred to the admirable discussions of Ganong and Lloyd.
Lists of the chemicals, apparatus, and supplies necessary for the
work outlined in this manual are given in Secs. 215, 216.
The cost of compound microscopes is the item of greatest
expense in the equipment of a laboratory, and their selection
4
GROWING PLANTS IN THE LABORATORY 5
demands careful thought. The laboratory should have enough
microscopes so that every student in a section may have his own
instrument. If this is not possible, it is better that the course
should be planned along such lines that the microscopie work
is largely in the nature of demonstrations by the instructor
on such microscopes as are available. Two or three students
working together at the same microscope create confusion and
secure poor results. There are a number of medium-priced instru-
ments on the market, with varying merits, from which the
instructor must choose for himself. A list of the more prominent
firms and agents is given in Sec. 218. It is false economy to
attempt to save expense on microscopes at the cost of workman-
ship and convenience in form. A set of microscopes may readily
be kept on the laboratory tables, protected from the dust when
not in use by paper cones, and used by successive sections,
although this system*demands much more watchfulness on the
part of the instructor than when each student has his own
instrument and is held responsible for its care.
GROWING PLANTS IN THE LABORATORY
Window sills and unused space should be utilized as far as
possible for keeping fresh and growing material alive in the
laboratory, not only for the interest that it arouses but also as
a practical matter of foresight which at times saves much diffi-
culty. Large jars covered with plate glass make excellent aquaria
and give little or no trouble. A surprising number of forms
will appear in them from time to time, and very interesting
cultures frequently become established. A glass growing case
(Wardian case) such as is described by Ganong, 7, p. 82, is a
most useful piece of equipment, and practically indispensable
for much physiological work when conservatories or greenhouses
are not available. A bay window shut off from the rest of
the room by tight glass screens is better still if the heat can
; be’ regulated.
6 LABORATORY METHODS AND EQUIPMENT
LABORATORY MATERIAL, PREPARATIONS, AND
COLLECTIONS
A laboratory should be kept well stocked with material and
slides sufficient for its work so that the instructor is never at a
loss for them. Some material and slides will probably have to be
purchased, and a list of dealers in botanical supplies is given in
Sec. 217. However, very many instructors will depend chiefly on
their own preparations and collections, and it is very desirable
that they do so. Material collected and prepared by oneself will
be generally better known and better taught than that from
dealers. The secret of keeping a laboratory well stocked is the
foresight which never loses the opportunity to preserve a fortu-
nate collection. The simpler methods of killing and preserving
material are given in Sec. 172. There are no great difficulties of
technique, and it is the experience of every botanist that mate-
rial will come to hand from time to time that is far better than
the average of that offered by the dealers. A laboratory should
always have large bottles of stock solutions of the simpler kill-
ing reagents (such as chrom-acetic acid) and preserving fluids
(such as alcohol) and a supply of wide-mouthed bottles and jars.
With this simple equipment at hand the instructor should be
constantly on the watch for opportunities to increase and improve
the laboratory stock. Thoughtfulness in this direction will save
much time and expense in the long run.
It is becoming desirable and even necessary to study many
points of detailed morphology and cell structure from slides.
These can be purchased singly or in sets from dealers (Sec. 217)
and the preparations are generally good ; however, the instructor
is urged to be self-reliant. The simpler methods of killing, im-
bedding, cutting, and staining are not difficult and are outlined
in the sections entitled Botanical Microtechnique. An advanced
student under direction can profitably be employed from time to
time in the service of slide making with excellent returns for the
expenditure involved. But more important is the added value
<a’
LABORATORY METHODS T
of working with material that is thoroughly familiar. There is
danger in depending too much on slides, and they should not be
used where the student may readily make temporary prepara-
tions, for much of the value of laboratory work lies in the devel-
opment in the student of a certain manual skill. It is, however,
still more important that he become acquainted with and study
material first-hand. Botany made too easy by doing for the stu-
dent what he can do for himself is botany robbed of certain of
its most obvious advantages as a laboratory study.
Some instructors are making considerable use of the lantern
and photographs, especially to illustrate ecological subjects, and
for this purpose they are of the greatest service. Large and
varied selections of lantern slides may be purchased (Sec. 219).
Charts have their evident value and there are some excellent,
although expensive, sets published (Sec. 219). It is not difficult
to make simple charts and diagrams even in colors (Ganong, T,
p. 115), and these may be adapted to the particular needs of the
course and cost almost nothing.
The herbarium and museum are most useful adjuncts to. the
laboratory. Especially important is demonstration material of
-~ groups which cannot be studied in many regions from living
a
plants, as, for example, the marine alge. Such material, either
in the form of herbarium sheets or on exhibition in museum
cases, forms a most useful part of the equipment of a botanical
department. The advantages of collections covering the local
flora are too obvious to need discussion. These matters are well
treated by Ganong, 7, Chapter VI.
LABORATORY METHODS
The laboratory work, with its accompanying notes, should
be kept absolutely separate from the text reading. Text-books
should not be allowed on the laboratory tables. Their function
is to present systematized accounts and conclusions after the
student has obtained a sufficient first-hand knowledge of the
8 LABORATORY METHODS AND EQUIPMENT
facts from the plants themselves, and to weld into one systematic
whole the somewhat isolated topics of laboratory study. It is
essential to good laboratory methods that the drawing and writing
of notes be done in the laboratory, which should be regarded as
a study room, like a library, open to the student as many hours
of the day as is possible, and every encouragement should be
given to extended individual work.
THE LABORATORY EQUIPMENT OF EACH STUDENT
Every student should have an individual equipment, kept
either in the drawers of the table or in lockers at the side of the
laboratory. The following essential instruments and supplies
had best be purchased by himself.
1. A razor, scalpel, forceps, and pair of needleés.
2. Slides and cover glasses.
3. Four solid watch glasses or salt dishes.
4. Two pipettes (medicine droppers), a camel’s-hair brush,
and a scale in centimeters, millimeters, and inches.
5. A medium pencil (4H) or two pencils, hard (6H) and rather
soft (3H), eraser, mapping pens, liquid India ink, red ink, and
blue ink. Several colored pencils will be found very useful if the
student is to construct diagrams illustrating life histories and other
topics (App., 18). Higgins’ red-label India ink runs more smoothly
and is generally more satisfactory than the waterproof ink.
6. Drawing paper and notebook. The drawings required may
be made on loose sheets kept in a folder, and the notes in a
book, but it has generally proved more convenient to use per-
forated sheets of both drawing paper and note paper, cut to the
same size, which can be loosely held together between stiff covers
by a string. Such paper can be purchased in blocks from certain
dealers (Sec. 218), or may be made up by a local stationer. The
drawing paper should take ink as well as fine pencil lines.
7. A hand lens is necessary unless the laboratory tables are
supplied with simple dissecting microscopes.
RECORDING NOTES 1 9
There should always be a general supply of glass tumblers,
plates, saucers, etc., to hold material, and a set of the simpler
reagents, such as iodine, eosin, acetic acid, potash solution,
glycerin, etc. (Secs. 169, 170) may be placed on each table.
GENERAL DIRECTIONS FOR THE STUDENT IN DRAWING
AND RECORDING NOTES
1. Plan your drawings so that every sheet covers a definite
subject or part of a subject and is not a mixture of unrelated
matter. There are three types of drawings, habit sketches,
diagrams, and detailed figures, which should never be combined
in the same outline. The habit sketch and diagrams treat of
general features, usually on a scale which makes it impossible
to show details, which, if included, would either be out of pro-
portion and inaccurate, or on too small a scale to be of value.
Treat the drawings as a form of expression which should have
the characteristics of good English, — namely, simplicity, clear-
ness, and accuracy.
2. Depend chiefly on accurate outlines. Shade as little as pos-
sible, and then simply and effectively (see Principles, Figs. 8,
- 20, 113, 134, 168, 247, 273, 299). Do not put in details which
you imagine but cannot see. Do not make objects appear more
geometrically regular than they really are; peas are not per-
fectly spherical, pith cells seen in section never have the outlines
of perfect hexagons, and so on.
: 8. Group your figures in an orderly manner, so that they tell a
consecutive story on the page, as illustrated in the Principles by
Figs. 8, 212, 270, and 299.
4, Ink drawings are more durable than pencil, but the manipu-
lation requires a sure touch and some delicacy of treatment.
They are best preceded by light pencil outlines, to establish
‘proportions, which may be erased when the figure is finished.
Use an India ink, diluted if necessary with weak ammonia
water so that it will flow smoothly. Ink drawings are worth
10 LABORATORY METHODS AND EQUIPMENT
trying and are generally favored by those with aptitude for
illustration.
5. Describe the figures either neatly in a legend at the bottom
of the sheet or on an accompanying page of the notes, using
letters to refer to the parts indicated. For sample legends see
Principles, Figs. 3, 57, 58, 59, 169, and 248. Give the approxi-
mate magnification when this is not evident. Explain in the
notes all the points not shown in the sketches, such as character-
istic color, consistency, ete. Think out everything before begin-
ning to write a description, and, if it is lengthy, draw up a brief
outline so that your notes have an orderly arrangement like the
form of an essay. Write the notes in connection with the mate-
rial and in the laboratory.
6. In describing an experiment record in separate paragraphs
what you did, what the results were, and your conclusions from
them. Do not leave out any little detail that may have influenced
the results ; for instance, if in a germination experiment the seeds
were allowed to get too dry. Make your record on the spot. Do
not go to the laboratory to observe the progress of an experiment
and write part or all of your notes elsewhere, but put down the
results in the presence of the materials and apparatus used.
7. If not original with yourself, always record the source from
which any statements were obtained, thus: “Experiment IX,
Results obtained by instructor in performing the experiment
before the class.”
8. Be neat and accurate. Forty pages of well-written, clearly
expressed, and exact notes are worth more than a hundred pages
of disorderly and inaccurate ones.
THE CONSTRUCTION AND USE OF THE CoMPOUND
MICROSCOPE
A. The chief parts of a compound microscope are :
1. The base which rests. on the table, generally horseshoe
in form.
pee NS
CONSTRUCTION OF THE MICROSCOPE sit
2. The stage, a horizontal shelf upon which is placed the
preparation or slide to be examined. The stage is attached
to the column.
3. The mirror, situated below the stage, by which the light is
reflected upward through the opening in the stage.
4. The diaphragm of various forms, frequently accompanied
by light condensers, attached to the lower side of the stage
and used to regulate the intensity of the light reflected by
the mirror.
5. The tube, a cylinder which holds the lenses and moves
up and down perpendicularly above the opening in the
stage. The tube is raised or lowered either by sliding it
back and forth with a turning movement or by a rack
and pinion mechanism. This mechanism is called the
coarse adjustment.
6. The fine adjustment, a milled head back of the tube,
which, on being turned, moves for a very short distance
the entire framework that holds the tube.
7. The lenses, of two sorts, — eyepieces or oculars which slip
into the upper end of the tube, and objectives which screw
in at the bottom. An important accessory to the tube is
the nose piece, capable of carrying two or three objectives
which may be revolved into place at the lower end of the
tube. A student’s microscope will generally be fitted with
two eyepieces, high and low, and with two objectives, high
and low, and these may be combined with one another to
give four grades of magnification ranging generally from
about 50 to more than 500 diameters. Ifthe objectives are
respectively 2 inch and 4 inch and the eyepieces 2 inches
and 1 inch, the lower objective with either eyepiece will
give a low power, the higher objective with the 2-inch eye-
piece a medium power, and the higher objective and 1-inch
eyepiece a high power.
8. The stand consisting of the microscope without the
lenses.
12
LABORATORY METHODS AND EQUIPMENT
B. To set the microscope up:
Jl
bo
Lift it out of its case by the lower part of the column to
which the stage is attached, never by the tube or where the
fine adjustment operates.
. Place it on the table with the fine adjustment nearest you.
. Screw the objectives into the nose piece and slip an
ocular into the upper end; turn the lowest power objec-
tive into position.
. Find the light by looking into the eyepiece and at the
same time turning the mirror at such an angle that it
reflects light from the window up through the opening in
the stage to the objective. When a clear, bright field is
obtained the microscope is set up.
. Regulate the quantity of the light by the diaphragm. If
too bright it must be cut off somewhat. The higher powers
require brighter light than the lower. Mirrors generally
have two faces, a plane and a concave. The concave mirror
is used with the high-power objectives.
C. To find the object:
ik
Place the slide on the stage, which should always be
horizontal, with the object over the middle of the opening
through which light is thrown from the mirror.
. With the lower power in position moye the coarse ad-
justment until either the object or small solid particles
on the slide appear distinctly, which means that the lenses
are in focus. The object, if not under the lens, may now be
brought into the field by moving the slide back and forth
very slowly. The focus of the coarse adjustment may gen-
erally be improved upon by the fine adjustment.
. To focus with the high-power objective, first find the
object with the low power and arrange in the center of the
field. Then turn the high-power objective into position. In
well-made instruments it will generally be found to come |
nearly into focus, and a slight movement of the fine adjust-
ment will show the object clearly. If not in focus, move
Pr. vere
USE OF THE MICROSCOPE 13
the tube slowly downward until the objective nearly
touches the slide, watching it carefully from the side, and
then raise it by the fine adjustment until the focus is es-
tablished. Never focus down with the high-power objec-
tive because of the danger of pressing it into the slide and
ruining the delicately mounted lenses.
D. Studying an object:
is
bo
Always examine an object first with the low powers so
as to understand its general structure before passing to
details.
. Obtain greater magnification, if the instrument permits,
by using more powerful objectives rather than higher eye-
pieces, for owing to peculiarities of the lenses clearer
images are thus obtained.
Do not rest satisfied until the light is of the best quality
obtainable with the mirror and diaphragm. It should not be
too bright. Details are shown more clearly by subdued light.
. Keep both eyes open in using a microscope. If this is
at first distracting, cover the free eye with the fingers
or by a paper screen projecting from the microscope tube
until it is no longer attracted by surrounding objects
on the table and the attention is entirely concentrated
: on the working eye. Never let the habit of squinting
develop.
. If it is necessary to ascertain the exact size of an object
this can best be done by the use of two micrometers. The
eyepiece micrometer consists of a disk of glass ruled with
fine equidistant lines; this is inserted beneath the upper
lens of the eyepiece. The stage micrometer is a glass slide
ruled with fine lines 1-100 mm. apart. To measure an
object the number of spaces on the eyepiece micrometer
which its image covers must be noted. Then the value of
each space is to be ascertained by substituting for the
object the stage micrometer. A simple calculation will
now give the diameter of the object.
we
14
LABORATORY METHODS AND EQUIPMENT
E. Rules for the use of the microscope:
ce
2.
3.
Never allow the objective to touch the cover glass or the
liquid in which the object is mounted.
Do not handle the front lens of the objective or unscrew
the sections in which the lenses are mounted.
Clean the front lens of the objective only when neces-
sary,and then with small pieces of lens paper, which should
be thrown away after use, or with an old clean, soft hand-
kerchief. Breathe on the lens before cleaning it, or, if that
is not sufficient, moisten the lens paper with a drop of
alcohol or xylol, taking care to wipe it perfectly dry as
quickly as possible.
. Do not let the objective remain long near volatile corro-
sive liquids such as hydrochloric or nitric acid or strong
solutions of iodine.
. Do not allow liquids to run from the slide over the stage
or other parts of the microscope.
. Keep the microscope covered with a bell jar or paper
cone when not in use, and keep the objectives and eye-
pieces away from dust.
Part l
STRUCTURE AND PHYSIOLOGY OF
SEED PLANTS
INTRODUCTORY STUDY OF A SEED PLANT
AND ITS ORGANS
1. The common dwarf nasturtium (Tropzolum).'
A. The plant body. Take a plant which has been carefully dug
up and note the division of the plant body into three sets
of parts or organs, roots, stems, and leaves, which constitute
its main bulk.
Make a reduced drawing to show the general form and
proportions of the entire plant. pd
B. Roots. Note the general form and arrangement of the roots
and the differences between roots and stem in size, shape,
color, and texture.
C. Stem. Make a reduced drawing of a portion of the stem,
with parts of two or three leafstalks, showing how they are
attached to it. Does thestem branch ? Is it solid or hollow ?
D. Leaves. Make a reduced drawing of one of the largest
leaves, including the leafstalk, and life-size drawings of two
or three of the youngest leaves near the tip of the stem.
Note the mode of attachment of the leafstalk to the expanded
portion, blade, of the leaf, the course of the veins through
the blade, and the differences between the upper and lower
surfaces of the latter.
1 Any plant with well-developed roots, stems, and leaves, and simple, conspicu-
ous flowers, will answer for this study. Good types available in autumn are the
garden balsam, the eo yellow oxalis (O. cymosa), the petunia, any of the
Gerardias, etc.
15
16 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
tive organs of the plant body, or the apparatus by which it
carries on the processes necessary for its life and growth.
In a general way it may be said that the roots serve to anchor
the plant and to absorb water and dissolved raw materials
from the soil to aid in the manufacture of plant food, that
the stem conducts water and plant foods, and that the leaves .
carry on most of the work of food making for the plant and
of admitting oxygen for respiration.
E. The flower. Note the occurrence of flowers at intervals along
the stem. Locate the points from which flowers may arise.
s
|
i
i
Roots, stems, and leaves taken together constitute the vegeta- .
|
Í
Sketch a short section of the stem with a flower attached.
Make a drawing of a flower (side view), noting the spur which
extends for some distance nearly parallel to the flower stalk.
Examine the outer surface and the inner surface of the |
flower to see how the somewhat leaf-like but bright-colored
parts which inclose it are related to each other. The five
outer portions together make up the calyx, and the five
inner ones the corolla. Calyx and corolla together consti-
tute the perianth. Cut away the members of the corolla
and note in the interior of the flower the eight curved stalks,
each surmounted by a knob, and within them a smaller |
object, split at the tip into three divisions. The knobbed
organs are stamens and the innermost organ is a pistil. |
F. The fruit. Find a series of old flowers in which the calyx
and corolla have become more and more withered, and trace
the development of the lower part of the pistil into a green
three-lobed fruit. Cut across a large, nearly dry fruit and find
out how many seeds are contained in each of its divisions.
2. Reproduction in the seed plant. Stamens and pistils taken
together constitute the reproductive organs of the plant. The
calyx and corolla aid the work of the stamens and pistils in
various mechanical and other ways.! The use of the flower is to `
bear seed, and seed formation is brought about by the action E
1 See Principles, Chapter XXXII.
THE SEED AND ITS GERMINATION 17
of the pollen (a substance produced by the stamens)? on the
rudimentary seeds, known as ovules, borne within the divisions of
the three-lobed base of the pistil.
3. Life history. The life history of every seed plant comprises
the series of changes which it undergoes in springing from a seed,
growing to maturity, and producing flowers and seed of its own.
THE SEED AND ITS GERMINATION
4. Germination of the squash seed.* * Soak some squash seeds in
tepid water for twelve hours or more. Plant these about an inch
deep in damp sand, pine sawdust, or peat moss, in a wooden box
which has had holes enough bored through the bottom to prevent
its holding water. Put the box in a warm place (not at any
time over 70°—80° Fahrenheit, or 21°-27° Centigrade), and cover
it loosely with a board or a pane of glass. Keep the sand or
sawdust moist, but not wet, and the seeds will germinate. As
soon as any of the seeds, on being dug up, are found to have
burst open, sketch one in this condition, noting the manner in
which the outer seed coat is split. Look for the peg, a kind of
knob, or hook, at the base of the hypocotyl, and see what it has
to do with the actions of the seedling. Continue to examine the
seedling at intervals of two days, until at least eight stages in
the growth of the plantlet have been noted.
Observe particularly how the sand is pushed aside by the rise
of the young seedlings. Suggest some reason for the manner in
which the sand is penetrated by the rising stem.
5. Examination of the squash seed.* * Make a sketch of the dry
seed, natural size.
A. Note the scar at the pointed end of the seed where the
latter was attached to its place of growth in the squash.
Label this ilum.
B. Note the little hole near the hilum; it is the micropyle, seen
most plainly in a soaked seed.
1 In the nasturtium the pollen is a yellow, rather sticky powder.
18 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
C. Describe the color and texture of the outer coating of
the seed. With a scalpel or a very sharp knife cut across
near the middle a seed that has been soaked in water for
twenty-four hours. Examine with the dissecting microscope
and sketch the section thus treated.
D. Taking another soaked seed, chip away the white outer
shell, called the testa, and observe the thin, greenish, inner
skin with which the kernel of the seed is closely covered.
E. Strip this off and sketch the uncovered kernel or embryo.
Note that at one end it tapers to a point. This pointed
portion, known as the hypocotyl, after the seed sprouts will
develop into the stem of the plantlet. Split the “halves” of
the kernel, seed leaves or cotyledons, entirely apart from each
other, and note where and to what extent they are connected.
F. Have ready some seeds which have been soaked for twenty-
four hours and then left in a loosely covered jar on damp
blotting paper at a temperature of 70° Fahrenheit (21° Centi-
grade) or over until they have begun to sprout. Split one of
these seeds apart, separating the cotyledons, and observe, at
the junction of these, two very slender pointed objects, the
rudimentary leaves of the plumule or first bud.
6. Examination of the bean. Study the seed, both dry and
after twelve hours’ soaking, in the same way in which the squash
seed has just been examined.
A. Notice the presence of a distinct plumule, consisting of a
pair of rudimentary leaves with a minute stem, between the
cotyledons, just where they are joined to the top of the
hypocotyl. In many seeds (as the pea) the plumule does
not show the distinct leaves, but in all cases it contains the
growing point, the tip of the stem from which all the upward
growth of the plant is to proceed.
B. Make a sketch of these leaves as they lie in place on one of
the cotyledons, after the bean has been split open.
Note the cavity in each cotyledon caused by the pressure of
the plumule and of the hypocotyl.
ed
RELATION OF TEMPERATURE TO GERMINATION 19
7. Examination of the pea. There are no very important points
of difference between the bean and pea, so far as the structure
of the seed is concerned, but the student should rapidly dissect
a few soaked peas to gain an idea of the appearance of the parts,
since he is to study the germination of the pea in detail.
Make only one sketch, that of the hypocotyl as seen in posi-
tion after the removal of the seed coats.
8. Germination of the bean (or the white lupine), the pea, and the
grain of corn.* ** Soak some beans or lupine seeds as directed in
Sec. 4, plant them, and make a series of sketches on the. same
general plan as those in Principles, Fig. 8.
Follow the same directions with some peas and some corn. In
the case of the corn, make six or more sketches at various stages
to illustrate the growth of the plumule and the formation of roots.
The student may be able to discover what becomes of the large
outer part of the embryo. This is believed to be the single coty-
ledon of the corn. It does not as a whole rise above ground, but
most of it remains in the buried grain, and acts as a digest-
ing and absorbing organ through which the endosperm, or food
stored outside of the embryo, is transferred into the growing
plant as fast as it can be made liquid for that purpose.
9. Germination of the horse-chestnut. Plant some seeds of the horse-
chestnut or the buckeye, study their mode of germination, and observe the
nature and peculiar modification of the parts.
EXPERIMENT I*
Relation of temperature to germination. sw ee at least four
beakers or tumblers, each with wet, soft paper packed in the
bottom to a depth. of nearly an inch. Have a tightly fitting
cover, such as a square of window glass or a “ clock glass,” over
* To THE InstRUCTOR: As some of the experiments upon seeds occupy a good
many days or weeks for their completion, the laboratory work should be pushed
on without waiting until these are finished. Results may be discussed from time
to time while the experiments are in progress and summed up when they are en-
tirely finished.
20 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
each. Put in each vessel the same number of soaked peas of about
the same size. Stand the vessels with their contents in places
where they will be exposed to different, but fairly constant, tem-
peratures, and the same conditions as regards light, and observe
the several temperatures carefully with a thermometer. Take
pains to keep the tumblers in the warm places from drying out,
so that their contents will not be less moist than those of the
others. The following series is merely suggested; other values
may be found more convenient. Note the rate of germination in
each place and record in tabular form as follows:
No. of seeds sprouted in 24 hr. 48 hr. 72 hr. 96 hr. ete.
At 32° F. (0° C.) —— ~— -—— -—
At 50° F. (10° C.) —— — — ——
ATORE (ELC)
At 90° F. (32° C.) ——
If a thermostat can be had, it should be used to control the
temperatures, and the highest point at which germination can
take place should be noted.
EXPERIMENT II
Amount of water in air-dry seeds and amount absorbed to produce germination.
A. Weigh accurately a convenient quantity of seeds, and then dry them
on the water bath until they no longer lose weight.1 Report the loss of
weight as water and calculate what per cent it constituted of the total
weight.
B. Weigh a new set of seeds from the original (undried) lot, place them
between layers of porous white paper kept thoroughly moist but not
dripping wet, cover them, and allow them to remain until the germina-
tion is evidently begun. Reweigh the seeds, and calculate the increase
of weight by absorption of water and the per cent of absorbed water.2
This last will be `
weight water absorbed
weight air-dry seeds —
1 This may be done once for all for the entire laboratory division. js
2? The gain in weight observed may be a trifle less than the total value, since
some loss of weight by oxidation is certain to have occurred.
STORAGE OF FOOD IN THE SEED 21
EXPERIMENT III
Will seeds germinate well without a good supply of air ? * *
A. Place some soaked seeds on damp blotting paper in the
bottom of a bottle, using seeds enough to fill it three quar-
ters full, and close tightly with a rubber stopper.
B. Put a few other seeds of the same kind in a second bottle,
and cover loosely. Place the bottles side by side, so that they
will have the same conditions of light and heat. Watch for
results and tabulate as in previous experiments.
EXPERIMENT IV
Effect of germinating seeds upon the surrounding air.** When
Exp. III has been finished remove a little of the air from above
the peas in the first bottle. This can easily be done with a rubber
bulb attached to a short glass tube. Then bubble this air through
some clear limewater made by slaking quicklime in warm water
and filtering through a paper filter. Also blow the breath through
some limewater by aid of a short glass tube. Explain any similar-
ity in results obtained. (Carbon dioxide turns limewater milky.)
Afterwards insert into the air above the peas in the same bottle
_ a lighted pine splinter, and note the effect upon its flame.
ia a. tie tae
STORAGE OF FOOD IN THE SEED
EXPERIMENT V
Are the cotyledons of a pea of any use to the seedling? Sprout
several peas on blotting paper. When the plumules appear
carefully cut away the cotyledons from some of the seeds. Place
on a wide, perforated cork one or two seedlings from which the
cotyledons have been cut, and as many- which have not been
mutilated. Put the cork in the mouth of a cylindrical glass jar
of water, which it should fit moderately well, and allow the roots
to extend into the water, which must be kept always at the same
level. Let them grow for some weeks and note results.
22 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
EXPERIMENT VI
Does the amount of material in the seed have anything to do with the rate
of growth of the seedling ? Germinate ten or more clover seeds, and about
the same number of peas, on moist blotting paper under a bell jar. After
they are well sprouted transfer both kinds of seeds to fine cotton netting,
stretched across wide-mouthed jars nearly full of water. Only the roots of
the seedlings should touch the water. Allow the plants to grow until the
peas are from four to six inches high.
10. Examination of the four-o’clock seed.1 Examine the external surface
of a seed of the four-o’clock,? and note the hardness of the outer coat. From
seeds which have been soaked in water at least twenty-four hours peel off
the coatings and sketch the kernel. Make a cross section of one of the
entire soaked seeds and sketch the section as seen with the magnifying
glass, to show the parts, especially the two cotyledons, lying in close contact
and encircling the white, starchy-looking endosperm. With a mounted needle
pick out the little almost spherical mass of endosperm from inside the coty-
ledons of a seed which has been deprived of its coats, and sketch the embryo,
noting how it is curved so as to inclose the endosperm almost completely.
11. Examination of the kernel of Indian corn.* * Soak some grains
of large yellow field corn for about two days.
A. Sketch an unsoaked kernel so as to show the grooved side,
where the germ lies. Observe how this groove has become
partially filled up in the soaked kernels.
B. Remove the thin, tough skin from one of the latter and
notice its transparency. This skin—the bran of unsifted
corn meal— does not exactly correspond to the testa and
inner coat of ordinary seeds, since the kernel of corn, like
all other grains (and like the seed of the four-o’clock), repre-
sents not merely the seed but also the seed vessel in which
it was formed and grew, and is therefore a fruit.
C. Cut sections of the soaked kernels, some transverse, some
lengthwise and parallel to the flat surfaces, some lengthwise
and at right angles to the flat surfaces. Try the effect of
staining some of these sections with iodine solution. Make
a sketch of one section of each of the three kinds, and label
1 Strictly speaking a fruit.
2 Morning-glory seeds or grains of buckwheat also answer well.
x
RECOGNITION OF SUBSTANCES IN PLANTS 23
the dirty white portion, of cheesy consistency, embryo; and
the yellow portions, and those which are white and floury,
endosperm.
D. Chip off the endosperm from one kernel so as to remove
the embryo free from other parts. Notice its form, some-
what triangular in outline, sometimes nearly the shape of
a beechnut, and in other specimens nearly like an almond.
Estimate what proportion of the entire bulk of the soaked
kernel is embryo (Principles, Fig. 378). Split the embryo
lengthwise so as to show the slender plumule.
12. Recognition of some chemical compounds found in plants.* * Out of the
very numerous substances which make up the framework of the plant body,
or are stored in it, there are several most important ones which the student
should be able to recognize by simple tests. In this place only starch, sugar,
cellulose, lignin, oil, and proteids will be discussed.
A. Starch. This turns blue, or nearly black, on the addition of iodine
solution. Make the test on a bit of laundry starch the size of a grain
of wheat diffused in a large test tube full of boiling water ; it does not
form a true solution, Add the iodine solution (Sec. 169) drop by drop
to the boiled starch after the latter has cooled.
B. Sugar. Some of the sugars found in plants produce a yellow or orange
color or an orange precipitate on being heated to boiling with a solution
of copper known as Fehling’s solution (Sec. 170). Cane sugar does not
give the reaction readily unless it has first been boiled with dilute
hydrochloric acid, when it responds promptly to the test. Make the
test with Fehling’s solution on a rather dilute solution of commercial
glucose in hot water.
C. Cellulose. This turns blue on being moistened with iodine solution
and then with concentrated sulphuric acid diluted with half its bulk
of water. Make the test with a bit of absorbent cotton (in this par-
ticular case wetting the cotton first with the acid and then with the
iodine solution).
D. Lignin. This substance, which forms a large part of the material of
lignified cell walls, gives a reddish violet color with phloroglucin solution
(Sec. 170) after the addition of hydrochloric acid. Make the test by
moistening a thin shaving of any kind of light-colored wood with a
solution of as much phloroglucin as can be taken up on the point of a
penknife in thirty or forty drops of 95 per cent alcohol. Then wet the
moistened shaving with a little concentrated hydrochloric acid.
24 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
E. Oil. Oils may be recognized by their characteristic appearance as seen
in minute droplets in the tissues of the plant when examined with the
microscope. Thin sections containing oil, when treated with ether or
chloroform, lose the oil almost instantly. Oils (and resins also) are
colored a deep red by the alcoholic solution of alkannin (Sec. 170) or of
the soluble material in alkanet root. Make the test on a thin section of
an oily seed (not Ricinus seed) placed under the microscope in an
alcoholic solution of alkannin.
F. Proteids. Proteids usually give a brick-red or rose-red color when
moistened with Millon’s reagent (Sec. 170) and gently heated. They
are stained yellow or brown by iodine solution. All proteids turn
yellow (xanthoproteic reaction) when moistened with strong nitric acid
and slightly warmed. The color deepens on the addition of ammonia
water to the stained substance. To make the nitric-acid test, warm a
little egg albumen with the strong acid, and when the coagulated
albumen becomes decidedly yellow pour off the excess of acid and
cover the stained mass with a little ammonia water.
Rererences. For the substances to be tested, Principles; Pfeffer, 31 ; for
the tests themselves, Zimmerman’s Botanical Microtechnique (Henry
Holt & Co., New York), and Strasburger-Hillhouse, 6.
EXPERIMENT VII
Occurrence of starch in seeds. Cut in two with a sharp knife the
seeds to be experimented on, and then pour on each, drop by
drop, some iodine solution. Only a little is necessary ; sometimes
the first drop is enough.
If starch is present a blue color (sometimes almost black) will
appear. If no color is obtained in this way, boil the pulverized
seeds for a moment in a few drops of water and try again.
Test in this manner corn, wheat (in the shape of flour), oats
(in oatmeal), barley, rice, buckwheat, flax, rye, sunflower, four-
o’clock, morning-glory, mustard seed (not ground mustard), beans,
peanuts, Brazil nuts, hazelnuts, and any other seeds that you can
get. Report results in tabular form.
REFERENCE. Strasburger-Hillhouse, 6.
13. Absorption of starch from the cotyledons. Examine with the micro-
Scope, using m.p. (medium power), thin sections of soaked beans and the ©
ea a a
STRUCTURE OF STARCH * 25
cotyledons from seedlings that have been growing for three or four weeks.
Stain the sections with iodine solution, and notice how completely the clusters
of starch grains that filled most of the cells of the unsprouted cotyledons have
disappeared from the shriveled cotyledons of the seedlings.
REFERENCES. Strasburger-Hillhouse, 6; Tschirch, 74.
14. Structure of starch.* *
A. Cut moderately thin sections of a potato tuber, mount in
water, and examine with m.p. (medium power). Note the
starch grains inclosed in little chambers or cells. Run in a
little weak iodine solution (Sec. 169) under one edge of the
cover glass, at the same time withdrawing water from the
opposite edge with a bit of blotting paper. Watch the sec-
tion carefully during the process and note the gradual stain-
ing of the starch grains. Draw.
B. Mount in water some pulp scraped from a freshly cut sur-
face of potato and examine with h.p. (high power). Move the
fine adjustment constantly while observing, and note the lines
arranged somewhat concentrically about a point called the
hilum, often marked by minute cracks in the grain. Draw
several grains.
Is there any evidence that the starch grain is composed of suc-
cessive layers? Ifso, how may they have been caused ?
©. Draw to the same scale as seen under h.p. all the principal forms and
sizes of potato starch grains that you can find, together with grains of
several other kinds, as canna starch (from the rootstock), oat starch,
corn starch, and Euphorbia starch (from E. splendens).
REFERENCES. Strasburger-Hillhouse, 6; Tschirch, 74.
EXPERIMENT VIII
Determination of oil in flaxseed. Weigh out two ounces (or sixty
grams) of ground flaxseed and add an equal volume of ether or
benzine. Do not bring these liquids near a gas jet or any other
flame. Let it stand ten or fifteen minutes and then filter. Wash
the meal by pouring over it, a little at a time, about the same
k
26 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
amount of liquid as was used at first. Let the liquid stand in a
saucer or evaporating dish in a good draft till it has lost the
odor of the ether or benzine. Weigh the remaining oil and cal-
culate what per cent of the ground seed was oil. (Traces will of
course still be left in the residue on the filter.)
Describe the oil which you have obtained. Of what use would
it have been to the plant ?
EXPERIMENT IX
Detection of proteids in seeds. Extract the germs from some
soaked kernels of corn and bruise them, or soak some wheat-germ
meal for afew hours in warm water, or in a stream of water wash
the starch out of wheat-flour dough; reserving the residue for
use, place it in a white saucer or porcelain evaporating dish and
moisten well and heat with Millon’s reagent (Sec. 170) or with
nitric acid; examine after fifteen minutes. Proteids turn yellow
when moistened with nitric acid and red with Millon’s reagent.
REFERENCE. Strasburger-Hillhouse, 6.
EXPERIMENT X
What plant foods are found in Brazil nuts? Crack several Brazil nuts, peel off
the brown coating from the kernel of each, and then grind the kernels to a
pulpinamortar. Shake up this pulp with ether, pour upon a filter paper, and
wash with ether until the washings when evaporated are nearly free from
oil. The funnel containing the filter should be kept covered as much as
possible until the washing is finished. Evaporate the filtrate to procure the
oil. Dry the powder which remains on the filter and keep it in a wide-mouthed
bottle. Test some of it for starch and for proteids. Does it appear that a
seed needs to contain both starch and oil, or may one replace the other ?
15. Microscopical study of reserve oil in a seed. Cut moderately thin
sections of an oily seed, e.g. peanut (not roasted). Mount in water and
examine with m.p. Note the cellular structure of the seed and the minute
oil globules within the cells. Try to estimate the number in a cell. Mount
another section in an alcoholic solution of alkannin or of the soluble portion
of alkanet root (Sec. 170). After a few minutes examine the section and note
STRUCTURE OF PROTEID GRAINS OF
the stained oil globules. Some larger droplets of oil may appear outside of
the section. Sketch, using h.p. if necessary.
REFERENCES. Strasburger-Hillhouse, 6; Tschirch, 74.
16. Structure of proteid grains (aleurone grains). A large part of the proteid
reserve material of seeds is stored in the form of minute bodies known as
aleurone grains. They occur in abundance packed around the starch grains
in such seeds as those of the bean and pea, but are more easily studied in
seeds nearly or quite free from starch. Remove the testa from a seed of
the castor-oil plant (Ricinus) and cut thin sections from the endosperm.
Mount in olive oil (which does not dissolve any of the proteid material) and
examine with h.p. Note the very small aleurone grains, each with a clear body
at the narrowend. Thisclear body, called the globoid, is of mineral material,
principally a double phosphate of lime and magnesia. Draw the aleurone
grains. Mount another section in water and examine ; then run in absolute
alcohol under one edge of the cover glass, and note the proteid crystal, which
should appear plainly, constituting a large part of the bulk of the aleurone
grain, and the globoid. The latter is now distinctly recognizable as a solid
substance. Draw.
_ Aleurone grains may be more easily demonstrated in thin sections of the
kernel of the Brazil nut. These should be rinsed twice in chloroform, to
remove the oil, then once in alcohol, and mounted in alcohol. Examine
with h.p., run in iodine solution while under the microscope, and note the
brown-stained grains in the cells. Draw.
REFERENCES. Strasburger-Hillhouse, 6; Tschirch, 74,
MOVEMENTS, DEVELOPMENT, AND MORPHOLOGY
i OF THE SEEDLING
EXPERIMENT XI
Is the arch of the hypocotyl due to the pressure of the soil on the rising
cotyledons? Sprout some squash seeds on wet paper under a bell glass, and
when the root is an inch or more long hang several of the seedlings, roots
down, in little stirrups made of soft twine, attached by a mixture of equal
parts of beeswax and rosin melted together to the inside of the upper part of
the bell glass. Put the bell glass on a large plate or sheet of glass on which
lies wet paper to keep the air moist. Note whether or not the seedlings form
= hypocotyl arches, and, if so, whether the arch is more or less perfect than
that formed by seedlings growing in earth, sand, or sawdust.
98 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
EXPERIMENT XII
The permanganate test, to distinguish root from hypocotyl. Make a solu-
tion of potassium permanganate in water by adding about 4 parts, by
weight, of the crystallized permanganate to 100 parts of water. Drop into
the solution seedlings of all the kinds that have been so far studied, each
in its earliest stage of germination (that is, when the root, or hypocotyl,
has pushed out of the seed half an inch or less), and also at one or two sub-
sequent stages. After the seedlings have been in the solution from three to
five minutes, or as soon as the roots are considerably stained, pour off (and
save) the solution and rinse the plants with plenty of clear water. Sketch
one specimen of each kind, coloring the brown-stained part, which is root,
in some way so as to distinguish it from the unstained hypocotyl. Note
particularly how much difference there is in the amount of lengthening in
the several kinds of hypocotyl examined. Decide whether the peg of the
squash seedling is an outgrowth of the hypocotyl or of the root.
EXPERIMENT XIII
In what portions of the root does its increase in length take
place? ** Sprout some peas on moist blotting paper in a loosely
covered tumbler. When the roots are one and a half inches or
more long, mark them along the whole length with equidistant
dots made with a bristle dipped in waterproof India ink, or a
fine inked thread stretched on a little bow of whalebone or
brass wire.
Fasten the peas with pins to moist blotting paper placed in a
vertical position under a bell glass or an inverted battery jar, and
examine the roots at the end of twenty-four hours to see along
what portions their length has increased ; continue observations
on them for several days.
Rererences. Detmer-Moor, 9; Pfeffer-Ewart, 31, IL; Darwin
and Acton, 11.
17. Review sketches. Make out a comparison of the early life
histories of all the other seedlings studied, by arranging in par-
allel columns a series of drawings of each, like those of Principles,
- Fig. 8, but in vertical series, the youngest of each at the top, thus: -
ROOTS 29
BEAN PEA CORN
First stage
Second stage
Third stage
Fourth stage
Fifth stage
Discuss their resemblances and differences.
ROOTS
18. Growth and microscopical examination of water roots. * *
A. Place some vigorous cuttings of Tradescantia, which can
usually be obtained of a gardener or florist, in a beaker or
30 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
jar of water. The jar should be as thin and transparent as
possible, and it is well to get a flat-sided rather than a cylin-
drical one. Leave the jar of cuttings in a sunny, warm place.
B. As soon as roots have developed at the nodes, and reached
the length of three quarters of an inch or more, arrange a
microscope in a horizontal position (Fig. 1) and examine the
| SCR SOE
im sll
Fic. 1. Microscope on ring stand
tip and adjacent portion of one of the young roots with a
power of from twelve to twenty diameters. Note:
(1) The root cap, of loosely attached cells.
(2) The central cylinder.
(3) The cortical portion, a tubular part inclosing the
solid central cylinder.
(4) The root hairs, which cover some parts of the outer
layer of the cortical portion very thickly. Observe
particularly how far toward the tip of the root the
root hairs extend, and where the youngest ones
are found.
oe ee i
ROOTS 31
Make a drawing to illustrate all the points above suggested
(1-4). Make a careful study of longitudinal sections through
the centers of the tips of very young roots of the hyacinth or
the “Chinese sacred lily.” 1 Sketch one section.
Make a study of the roots of any of the common duckweeds,
growing in nutrient solution (No. 1, Exp. XV) in a jar of water
under a bell glass, and note the curious root pockets, which here
take the place of root caps.
REFERENCES. Strasburger-Hillhouse, 6; Strasburger, Noll,
Schenk, Karsten, 1.
19. Structure of the central cylinder of a monocotyledonous root.* * Cut thin
cross sections of the adventitious roots of onion or hyacinth near their bases. ?
Examine these in water with a power of two hundred or more diameters.
The central cylinder or stele shows in the cross section as a nearly circular
area containing a few large openings and many smaller ones. The largest open-
ings are usually only one or two in number and represent the large vessels
cut across. These are tubes with a diameter of 4,5 to 73, of an inch, with
ladder-like markings (seen only in the longitudinal section) on their walls.
Radiating away from these are the openings of (in the onion) six other ves-
sels of about half the diameter of the central vessels and with similar mark-
ings. Just outside of each of the’six vessels is an irregular group “of much
smaller vessels with spiral markings (seen on longitudinal section). The
openings of the vessels form on the cross section of the central cylinder an
irregular six-rayed star, and the spaces between the rays are mainly filled by
sieve tubes or soft bast, separated from the vessels of the wood system by
parenchyma cells. The outermost portion of the central cylinder consists of
a single layer of cells constituting the pericycle, and this is surrounded by
the innermost layer of the primary cortex, the endodermis.
REFERENCE. Strasburger-Hillhouse, 6.
20. Structure of the dicotyledonous root; secondary thickening.* The struc-
ture of very young dicotyledonous roots is often similar in most respects
to that of the onion root (Sec. 19).4 Secondary thickening (Principles, Sec. 80)
1 Narcissus Tazetta, var. orientalis. '
2 These roots may be obtained from an onion or a hyacinth bulb set in a tum-
blerful of water and left in a warm place until the roots are well developed. They
may also be taken from hyacinth plants growing in pots, by inverting the latter,
removing the contents, and replacing the plant when the needed material has been
secured from it.
8 This section may to advantage be deferred until after Sec. 31.
4 Good materials for study are roots of Ranunculus, bean, or (very young)
grapevines.
32 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
soon occurs in the roots of dicotyledonous trees and shrubs, and the structure
of such roots considerably resembles that of the stem, except that pith is
frequently lacking.
With the lens examine cross sections of large roots of any hardwood tree.
Note the annual rings of wood and their porosity, due to the presence of
many and large vessels. The cortical part sometimes (as in sassafras) forms
a thick bark. x
With the microscope examine thin cross sections, stained with phloro-
glucin (Sec. 12, D), of the tap root of a seedling hardwood tree not more
than a year old.1 Use first l.p., then m.p. Note the division of the root
into a cortical region or bark,wood, and (sometimes) pith. Note the relatively
small amount of wood in the younger portions of the root, increasing in the
older parts. Make drawings to illustrate this point. Make a drawing of a
quarter or less of one of the older sections, showing the distribution of mate-
rial from center to exterior. In your drawing color the lignified hard-bast
fibers of the bark (Sec. 29, C) and the wood fibers, to distinguish them from the
non-fibrous parenchyma which makes up much of the bulk of the young root.
If the material was collected in the autumn or winter, test a section with
iodine solution for starch, and if any is found describe its distribution.
REFERENCES. Strasburger-Hillhouse, 6; Strasburger, Noll, Schenck,
Karsten, 1; Tschirch, 83.
21. Examination of a fleshy root. Cut a parsnip across below
the middle, and stand the cut end of the upper part in eosin solu-
tion (Sec. 169) for twenty-four hours.
A. Examine by slicing off successive portions from the upper
end. Sketch some of the sections thus made. Cut one pars-
nip lengthwise and sketch the section obtained. In what
portion of the root did the colored liquid rise most readily ?
The ring of red marks the exterior of the central cylinder
in contact with the cortical portion. To which does the
main bulk of the parsnip belong ?
B. Cut thin transverse sections from an eosin-stained parsnip
and notice how the medullary rays run out into the cortical
portion, and in those sections that show it find out where
the secondary roots arise.
1 These may be planted for the purpose, but usually it is easy to find plenty EA 4
young seedling cherries, birches, elms, ashes, maples, etc.
MINERAL SUBSTANCES REQUIRED BY PLANTS 33
C. If possible, peel off the cortical portion from one stained
root and leave the central cylinder with the secondary roots
attached. Stain one section with iodine and sketch it.
Where is the starch of this root mainly stored ?
D. Test some bits of parsnip for proteids by boiling them for
a minute or two with strong nitric acid.
What kind of plant food does the taste of cooked parsnips
indicate? [On no account taste the bits which have been
boiled in the poisonous nitric acid. ]
EXPERIMENT XIV.
Percentage of water in the plant body. Take any such soft portions of seed
plants as the roots of carrots or turnips, shoots of asparagus, and leaves of
lettuce or spinach, or cut off a green herbaceous plant at the level of the
ground, Slice the roots and stems as thin as possible and pick the leaves to
pieces. Weigh out convenient portions at once to avoid drying, place each
portion in a water bath, and heat until no further loss of weight takes place.
It will save much time and render the experiment more accurate if the
materials are in each case kept ina shallow vessel, such as a large watch
glass, throughout the process of drying and the weighings. Finally calculate
_ from the loss of weight the percentage of water originally present.
EXPERIMENT XV
What mineral substances are required by ordinary seed plants ? * *
A. Prepare a nutrient solution (No. 1) containing for every 1500 parts
by weight (grams) of water! the following amounts of salts:
Grams
(CUCM TNER TR lame EPs. ay Ronn cr
Potassium chloride . 4
Magnesium sulphate : 4
Acid potassium phosphate (KHz PO,) . : 4
Merhicchlovidesolution., esns « w son im `A ew drow
Prepare several glass cylinders of the capacity of a pint or more by
rinsing out with strong nitric acid and then with plenty of water.
1 Distilled water which has been prepared in a glass, porcelain, or block tin
distilling apparatus and then aérated by shaking up with air should be used.
Very pure rain water collected from a thoroughly washed roof will answer
equally well.
34 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
B. Make another nutrient solution (No. 2) like No. 1, but without iron ;
another (No. 3) containing the same ingredients as No. 1, except the cal-
cium nitrate, for which one gram of calcium sulphate is to be substi-
tuted; and another (No. 4) like No. 1, except that acid sodium phosphate
is to be substituted for the acid potassium phosphate.
C. Place in each jar a vigorous young wheat seedling with only its roots
submerged, or a cutting of Tradescantia. Cover each jar with a piece of
pasteboard wrapped around the glass so as to exclude light from the
solution and put all the jars in a warm place but not in full sunlight.
Change the nutrient solution every week and continue the culture for
four or five weeks. If the roots seem dirty and slimy, allow the plants
to stand for a day or two at a time with the roots in distilled water or
a weak solution of calcium sulphate.
D. At the end of the period sketch all the plants and label as follows:
1. Culture in full nutrient solution.
2. Culture without iron.
8. Culture without nitrogen.
4. Culture without potassium.
What conclusions can you draw from the experiment ?
REFERENCES. Detmer-Moor, 9; Pfeffer-Ewart, 31, I; Peirce, 32.
EXPERIMENT XVI
Effect of diminished temperature on absorption of water by roots.
A. Transplant a tobacco seedling about four inches high into rich earth
contained in a narrow, tall beaker or very large test tube (not less
than 1} inch in diameter and six inches high).
B. When the plant has begun to grow again freely in a warm, sunny room,
insert a chemical thermometer into the earth ; this can best be done by
making a hole with a sharp, round stick, pushed nearly to the bottom of
the tube, and then putting the thermometer in the place of the stick.
Water the plant well, and then set the tube in a jar of pounded ice which
reaches nearly to the top of the tube. Note the temperature of the earth
just before placing it in the ice. Cover the ice with cotton batting or a
piece of flannel so that the stem and leaves of the plant will not be
chilled by the proximity of the ice.
C. Observe whether the leaves of the seedling wilt, and if so, at what
temperature the wilting begins.
D. Finally, remove the tube from the ice and place it in warm water
(about 80° F. or 27° C.). Observe the effect and note the temperature
at which the plant, if wilted, begins to revive. :
grown out horizontally,
DOWNWARD GROWTH OF THE ROOT 35
E. Find an average between the wilting temperature and the reviving
temperature. For what does this average stand? Repeat the experi-
ment with oat seedlings.
REFERENCE. Pfeffer-Ewart, 31, I.
EXPERIMENT XVII
Do all parts of the root of the Windsor bean seedling bend downward alike ?
Fasten some sprouting Windsor beans with roots about an inch in length to
the edges of a thick disk of pine wood or other soft wood in a soup plate partly
full of water and cover them with a low bell jar.
Steel pins run through the cotyledons, as in Fig. 2, will hold the beans in
place. Mark the roots, as in Exp. XIII, to see in what region the bending
occurs ; that is, whether in the older part or by the addition of new material
at the tip. When the roots have begun to point downward strongly, turn
most of the beans upside down and pin them in the reversed position. If
you choose, after a few days reverse them again. Make sketches of the vari-
ous forms that the roots assume and discuss these.
REFERENCES. Detmer-Moor, 9; Pfeffer-Ewart, 31, III.
EXPERIMENT XVIII
Does the Windsor bean root tip press downward with a force greatet than its
own weight? Arrange a sprouted bean as shown in Fig. 2,! selecting one
that has a root about twice
as long as the diameter of
the bean and that has
having been sprouted on a
sheet of wet blotting paper.
The bean is pinned to a
cork that is fastened with
beeswax and rosin mixture
to the side of alittle trough Fie. 2. A sprouting Windsor bean pushing its
_ or pan of glass or glazed root tip into mercury
earthenware. The pan is s, seed; r, root; w, layer of water; m, mercury
filled half an inch or more After Sachs
with perfectly clean mer-
cury, and on top of the mercury is a layer of water. The whole is closely
covered by a large tumbler or a bell glass. Allow the apparatus to stand
until the root has forced its way down into the mercury. Then run a slender
1 Or see Ganong, 10.
36 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
needle into the root at the level of the mercury (to mark the exact level),
withdraw the root, and measure the length of the part submerged in mercury.
To see whether this part would have stayed under by virtue of its own weight,
cut it off and lay it onthe mercury. Push it under with a pair of steel for-
ceps and then let go of it. What does it do ?
EXPERIMENT XIX
What causes the root to go downward ?
A. Pin some soaked Windsor beans to a large flat cork, cover them with
thoroughly moistened chopped peat moss, and cover this with a thin
glass crystallizing dish. Set the cork on edge.
B. Prepare another cork in the same way, attach it to a clinostat, and
keep it slowly revolving in a vertical position for from three to five
days. Compare the directions taken by the roots on the stationary and
on the revolving cork.
REFERENCES. Ganong, 10; Pfeffer-Ewart, 31, II.
22. Propagation by means of roots. Bury a sweet potato or a
dahlia root in damp sand and watch the development of sprouts
from adventitious buds. One sweet potato will produce several
crops of sprouts, and every sprout may be made to grow into a
new plant. It is in this way that the crop is started wherever
the sweet potato is grown for the market.
SOME PROPERTIES OF CELLS AND THEIR
FUNCTIONS IN THE ROOT
EXPERIMENT XX
Osmosis as shown in an egg.
A. Cement to the smaller end of an egg a bit of glass tubing about six
inches long and about three sixteenths of an inch in inside diameter. A
mixture of equal parts of beeswax and rosin melted together makes
the best cement for this. Chip away part of the shell from the larger
end of the egg, place it in a wide-mouthed bottle or a small beaker full
of water (as shown in Principles, Fig. 28), and then very cautiously
pierce a hole through the upper end of the eggshell by pushing a
knitting needle or wire down through the glass tube. Watch the
EXPERIMENTS ON OSMOSIS Su
apparatus for some hours and note any change in the contents of the
tube or the beaker.! Explain.
The rise of liquid in the tube is evidently due to water making its
way through the thin membrane which lines the eggshell, although
this membrane contains no pores visible even under the microscope.
B. An alternative experiment is to fasten a pig’s bladder or a diffusion
shell (obtainable of dealers in chemical and physical apparatus) to the
end of a glass tube six or eight feet long. For a §-inch (16-mm.)
diffusion shell the tube should be $-in. outside diameter; for the
bladder a tube must be chosen that barely enters the opening in it.
A tight joint is more certainly secured by using a tube a little smaller
than is needed to enter the opening in the shell or bladder, slipping
over the tube a bit of rubber tubing an inch or more long, inserting
this in the shell and wiring it tightly with rather fine copper wire.
Fasten the tube upright, with the diffusion membrane submerged in a
large jar of water, and pour into the open end of the tube enough
molasses to remain visible above the diffusion membrane. A rather
large tube may be filled through a slender funnel, taking pains not to
let the molasses stick to the sides as it descends. A narrow tube must
be filled before tying into the neck of the bladder, the free end of the
tube corked, and the other end then tied in place. Note any change of
level in the molasses in the tube.?
REFERENCES. Ganong, 10; Detmer-Moor, 9; Pfeffer-Ewart, 31, I.
EXPERIMENT XXI
Result of placing sugar on a begonia leaf. Put a little powdered
. sugar on the upper surface of a thick begonia leaf under a small
bell glass. Put another portion of sugar on a bit of paper along-
side the leaf. Watch for several days. Explain the results. The
upper surface of this leaf contains no pores, even of micro-
scopic size.
STEMS
23. The horse-chestnut or buckeye twig.* * Procure a twig of
_horse-chestnut eighteen inches or more in length. Make a careful
sketch of it, trying to bring out the following points:
A. The general character of the bark.
1 Testing the contents of the beaker with a solution of nitrate of silver will then
show the presence of more common salt than is found in ordinary water.
j 2 A still more instructive experiment is that on plasmolysis of the Spirogyra
cell (Sees. 56, D, and 57, C).
88 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
B. The large horseshoe-shaped scars and the number and posi-
tion of the dots on these scars. Compare a scar with the
base of a leafstalk furnished for the purpose.
C. The ring of narrow scars around the stem in one or more
places, and the different appearance of the bark above and
below such a ring.! Compare these scars with those left
after removing the scales of a terminal bud.
D. The buds at the upper margin of each leaf scar and the
strong terminal bud at the end of the twig. The dots on the
leaf scars mark the position of the ducts and wood cells in
the fibro-vascular bundles which run from the wood of the
branch through the leafstalk up into the leaf.
E. The flower-bud scar, a concave impression to be found in
the angle produced by the forking of two twigs, which form,
with the branch from which they spring, a Y-shaped figure.
F. The place of origin of the twigs on the branch (on a branch
larger than the twig handed round for individual study) ;
make a separate sketch of this.
The portion of a stem which originally bore any pair of leaves
is a node, and the portions between the nodes are internodes.
Describe briefly in writing alongside the sketches any observed
facts which the drawings do not show.
If your twig was a crooked, rough-barked, and slow-growing
one, exchange it for a smooth, vigorous one, and note the differ-
ences. Or if you sketched a quickly grown shoot, exchange for
one of the other kind.
Questions. 1. How many inches did your twig grow during
the last summer? How many during the summer before?
How do you know? How many years old is the whole twig
given you?
2. How were the leaves arranged on the twig? How many
leaves were there? Were they all of the same size?
Instead of beech, as denorthod in the nent aseeiony paniya at) aan
butternut, black walnut, poplar, or cottonwood will do. The rings are especia y
well shown by cherry, apple, pear, cottonwood, or aspen. j l
STEMS AND STEM STRUCTURE 39
3. What has the mode of branching to do with the arrangement
of the leaves ? with the position of the flower-bud scars ?
24. Twig of beech.
A. Sketch a vigorous young twig of beech (or of hickory,
magnolia, or tulip tree) in its winter condition, noting par-
ticularly the respects in which it differs from the horse-
chestnut. Describe in writing any facts not shown in the
sketch. Notice that the buds are not opposite, nor is the
next one above any given bud found directly above it, but
part way round the stem from the position of the first one.
B. Ascertain, by studying several twigs and counting around,
which bud is above the first and how many turns round the
stem are made in passing from the first to the one directly
above it.
C. Observe with especial care the difference between the beech
and the horse-chestnut in mode of branching, as shown in a
large branch provided for the study of this feature.
STRUCTURE OF THE STEM
Stem or MONOCOTYLEDONOUS PLANTS
25. Gross structure of the corn stem.* * Refer to the sketches of
the corn seedling to recall the early history of the corn stem.
A. Study the external appearance of a piece of corn stem or
bamboo two feet or more in length. Note the character of
the outer surface. Sketch the whole piece and label the
enlarged nodes and the nearly cylindrical internodes.
B. Cut across a corn stem and examine the-cut surface with
the lens. Make some sections as thin as they can be cut
and examine with the lens (holding them up to the light)
or with a dissecting microscope. Note the firm rind com-
posed of the epidermis and the underlying tissue, the large
1This may be made clearer by winding a thread about the twig, making it
touch the base of each bud.
40 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
mass of pith composing the main bulk of the stem, and the
many little harder and more opaque spots, which are the
cut-off ends of the woody threads known as jfibro-vascular
bundles.
C. Split a portion of the stem lengthwise into thin, translucent
slices, and notice whether the bundles seem to run straight up
and down its length; sketch the entire section (x 2). Every
fibro-vascular bundle of the stem passes outward through
some node in order to connect with some fibro-vascular
bundle of a leaf. Knowing this fact, the student would
expect to find the bundles bending out of a vertical position
more at the nodes than elsewhere. Can this be seen in the
stem examined? Observe the thickening at the nodes, and
split one of these lengthwise to show the tissue within it.
D. Compare with the corn stem a piece of palmetto and a piece
of cat brier (Smilax rotundifolia, S. hispida, etc.), and notice
the similarity of structure. Compare also a piece of rattan
and of bamboo.
Minute structure.
E. Stain a thin cross section! with phloroglucin (Sec. 12, D) and sketch with
m.p. one of the larger bundles (some distance in from the rind). In your
drawing color the stained portions, which represent the lignified scleren-
chyma fibers. Look for stained rigid tissue (sclerenchyma) in the rind.
F. Cut several very thin longitudinal sections from a piece of stem not more
than one-fourth to one-third inch long, split through the middle. Stain
with phloroglucin and make a drawing of the best bundle found. Note
the two kinds of vessels, or vessel-like tracheids, some with spiral
threads lining the interior, and others with transverse rings. Separate
rings are often seen detached from their vessels and beautifully stained
by the phloroglucin.
Rerrrences. Strasburger-Hillhouse, 6; Strasburger, Noll,
Schenck, Karsten, 1. .
A more complicated kind of monocotyledonous stem structure
can be studied to advantage in- the surgeons’ splints cut from
yucca stems and sold by dealers in surgical supplies.
1 Asparagus stem may also be used. Tn adt sano
-
STRUCTURE OF STEMS 41
Stem or DicotyLeponous PLANTS
26. Gross structure of an annual dicotyledonous stem. **
A. Study the external appearance of a piece of sunflower stem
several inches long. If it shows distinct nodes, sketch it.
B. Examine the cross section with the lens and sketch it.
After your sketch is finished compare it with Principles, hee
56, which probably shows more details than your drawing,
and label the parts shown as they are labeled in that figure.
C. Split a short piece of the stem lengthwise through the i
center and study the split surface with the lens. Take a `
sharp knife or a scalpel and carefully slice and then scrape
away the bark until you.come to the outer surface of a
bundle.
D. Examine a vegetable sponge (Luffa), sold by druggists,
and notice that it is simply a network of fibro-vascular
bundles. It is the skeleton of a tropical seed vessel or fruit,
very much like that of the wild cucumber common in the
central states, but a great deal larger.
Structure of bark. The different layers of the bark cannot all be well recog-
nized in the examination of a single kind of stem. With lens examine:
E. The cork which constitutes the outer layers of the bark of cherry or
birch branches two or more years old. Sketch the roundish or oval
lenticels on the outer surface of the bark. How far in do they extend ?
F. The green layer of bark as shown in twigs or branches of Forsythia,
‘cherry, alder, box elder, wahoo, or willow.
G. The white, fibrous inner layer, known as hard bast, of the bark of elm,
leatherwood, or basswood.
27. Minute structure of the ordinary dicotyledonous stem. Cut thin cross
sections of the stem of one of the perennial species of sunflower (Helianthus),
or any large composite. Stain by immersing for a few seconds in a half-
saturated aqueous solution of safranin, then wash, and examine in water,
first with l.p. and then with m.p. The structural elements of the stem are
considerably differentiated by the stain, the outer layers of the cortex ap-
pearing yellowish brown, the hard bast magenta, the wood fibers reddish
magenta, and the pith salmon color.
Rererences. Strasburger-Hillhouse, 6; Strasburger, Noll, Schenck,
Karsten, 1.
42 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
28. Minute structure of the climbing dicotyledonous stem.* *
A. Study, first with l.p. and then with m.p., thin cross sections
of clematis stem? cut before the end of the first season’s
growth. Sketch the whole section without much detail, and
then make a detailed drawing of a sector running from cen-
ter to circumference and just wide enough to include one of
the large bundles. In general label these drawings, as in
Figs. 57 and 58 of the Principles. Note:
1. The general outline of the section.
2. The number and arrangement of the bundles. (How
many kinds of bundles are there?)
3. The comparative areas occupied by the woody part of
the bundle, and that which belongs to the bark.
4. The way in which the pith and the outer bark are con-
nected (and the bundles separated) by the medullary rays.
B. Examine a longitudinal section of the same kind of stem
to find out more accurately of what kinds of cells the pith,
the bundles, and the outer bark are built. Which portion
has cells that are nearly equal in shape, as seen in both
sections ?
REFERENCES. Strasburger-Hillhouse, 6; Strasburger, Noll,
Schenk, Karsten, 1.
29. Kinds of cells which compose stems.? Examine with m.p. these prepara-
tions (A-J below). Study very carefully each of the required sections, find
in it the kind of cell referred to, and make a good drawing of a group of
cells of each kind.
A. Very thin sections of the outside layers of the cortex of a potato,
some cut tangential to the outer surface, other sections cut at right
angles to it (cork).
B. Thin sections of the green layer of the bark of Forsythia, Euonymus,
or box elder (Negundo) (green cells of cortical parenchyma).
C. Thin cross sections and lengthwise sections of the inner bark of
linden twigs. Test with phloroglucin (hard bast).3
1 Clematis virginiana is simpler in structure than some of the other woody
species. Aristolochia or Memispermum sections will do very well. If unmounted
sections are studied, stain with phloroglucin (Sec. 12, D). See also Sec. 138, B.
3 Both hard-bast fibers and wood fibers are known as sclerenchyma, but they
differ somewhat in appearance and much in location.
ie
STEM STRUCTURE 43
D. Lengthwise sections of the stem of squash or cucumber plants (sieve
cells or soft bast).
E. Thin cross sections of young twigs of pine or oak, collected and pre-
served in late summer (cambium).
F. Thin cross sections and lengthwise sections of apple, plum, maple, or
box-elder wood. Test with phloroglucin (wood jfibers).1
G. Thin lengthwise sections of any coniferous wood. ‘Test with phloro-
glucin (tracheids). é
H. Thin lengthwise sections of the stem of castor-oil plant (Ricinus) or
of banana fruit stalks (vessels).
I. Thin lengthwise radial sections of sycamore, sassafras, or red-cedar
wood (wood parenchyma).
J. Thin sections of pith of the stem of elder or sunflower (pith cells).
REFERENCES. Strasburger-Hillhouse, 6; Strasburger, Noll, Schenck,
Karsten, 1. 8
30. Comparative structure of monocotyledonous and dicotyledonous bundles.* *
Examine with a power of about 150 diameters :
A. The cross section of a bundle of the corn stem stained with phloro-
glucin.
B. The cross section of a bundle of Aristolochia stem,? stained with
phloroglucin,
Decide by referring to your drawings in Secs. 25, 28, which is the outer
part of each bundle. Observe the number and position of the area made up
of lignified fibers (stained by the phloroglucin), the cambium (in B), and the
sieve tubes. These tubes are less easy to identify than most of the other
elements of the bundles, but may be known by their location: in A, partly
between but mostly outward (toward the rind) from the pair of large
vessels ; in B, just outside the cambium of the bundle. Note the general
resemblance between the two kinds of bundles, with the presence of cambium
in B as much the most important point of difference between them.
31. The dicotyledonous stem, thickened by secondary growth.
A. Cut off, as smoothly as possible, a small branch of hickory
and one of white oak above and below each of the rings of
scars already mentioned, and count the rings of wood above
and below each ring of scars. How do the numbers corre-
spond ? What does this indicate ?
1 Both hard-bast fibers and wood fibers are known as sclerenchyma, but they
differ somewhat in appearance and much in location.
2 This section should be made from a young stem collected and preserved dur-
ing the early part of the summer.
44 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
B. Count the rings of wood on the cut-off ends of Iarge billets
of some of the following woods: locust, chestnut, sycamore,
oak, hickory. Do the successive rings of the same tree agree
in thickness ?. Why or why not? Does the thickness of
the rings appear uniform all the way round the stick of
wood ? If not, the reason in the case of an upright stem
(trunk) is perhaps that there was a greater spread of leaves
on the side where the rings are thickest (Principles, Fig. 76).
Plant food, in the case of trees, is mainly produced in the
leaves, and the course through the trunk of sugar or other
food in solution is mainly straight down along the sieve
tubes of the young wood. This would account for more rapid
growth on the more leafy side. Sometimes the inequality
may be because there was unequal pressure caused by bending
before the wind. Do the rings of any one kind of tree agree
in thickness with those of all the other kinds? What does
this show?
C. In all the woods examined look for:
1. Contrasts in color between the heartwood and the sapwood.
2. The narrow lines running, in very young stems, pretty
straight from pith to bark ; in older wood extending only a
little of the way from center to bark,—the medullary rays.
. The wedge-shaped masses of wood between these.
4. The pores which are so grouped as to mark the divisions
between successive rings. These pores indicate the cross
sections of vessels or ducts. Note the distribution of the
vessels in the rings to which they belong, and decide at
what season of the year the largest ducts are mainly pro-
duced. Make a careful drawing of the end section of one
billet of wood, natural size.
D. Cut off a grapevine several years old and notice the great
size of the vessels.
E. Examine the smoothly planed surface of a billet of red oak
that has been split through the middle of the tree, and note
the large, shining plates formed by the medullary rays.
wo
COURSE OF WATER IN STEMS 45
WORK OF THE STEM
EXPERIMENT XXII
Course of water in stems.* *
“A. Cut some short branches from an apple tree or a cherry
tree, and stand the lower end of each in eosin solution; try
the same experiment with twigs of oak, ash, or other porous
wood, and after some hours! examine with the lens and with
the microscope, using l.p., successive cross sections of one or
more twigs of each kind. Note exactly the portions through
which the eosin has traveled. Pull off the leaves from one
of the stems after standing in the eosin solution, and notice
the spots on the leaf scar through which the eosin has trav-
eled. These spots show the positions of the leaf traces, or
fibro-vascular bundles, connecting the stem and the leaf.
B. Repeat with several potatoes cut crosswise through the
middle.
C. Try also some monocotyledonous stems, such as those of
the lily or asparagus.
\D. For the sake of comparison between roots and stems treat
any convenient root, such as a parsnip, in the same way.
Examine the longitudinal sections of some of the twigs, the
potatoes, and the roots. In drawing conclusions about the
channels through which the eosin has risen (those through
which the newly absorbed soil water most readily travels),
bear in mind the fact that a slow soakage of the eosin will
take place in all directions, and therefore pay attention only
to the strongly colored spots or lines.
What conclusions can be drawn from this experiment as to
the course followed by the soil water ?
REFERENCES. Detmer-Moor, 9; Ganong, 10; Strasburger, Noll,
Schenck, Karsten, 1; Pfeffer-Ewart, 31, I.
1 If the twigs are leafy and the room is warm, only from five to thirty minutes
may be necessary. The experiment may be performed with a translucent-stemmed
plant like Impatiens Sultani, and the course of the eosin watched. See‘Ganong, 10.
7 oo
Ee j a
46 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
EXPERIMENT XXIII
What effect does loss of water have on the firmness of plant
tissues ? How long does it take for the water to be restored ?
A. Allow a fuchsia or a hydrangea? which is growing in a
flowerpot to wilt considerably for lack of water.
B. Then water it freely and record the time required for the
leaves to begin to recover their natural position and the
time to recover fully. The time needed for the leaves to
begin to resume their ordinary position is that consumed in
entering the roots (largely through the root hairs) and push-
ing upward through the stem until the water pressure in the
leaves is restored to its normal amount. Filling the leaf
cells fuller of water (increasing their turgor) has the same
effect on their firmness that inflating a football or a bicycle
tire does upon its firmness.
REFERENCE. Pfeffer 31, I.
32. Examination of twigs for starch. Cut thin cross sections of twigs of
some common deciduous tree or shrub in its early winter condition, moisten
with iodine solution, and examine for starch with a moderately high power
of the microscope. Sketch the section with a pencil, coloring faintly the
starchy portions with blue ink, used with a mapping pen, and describe
exactly in what portions the starch is deposited.
33, A typical tuber: the potato. Sketch the general outline of
a potato, showing the attachment to the stem from which it grew.?
A. Note the distribution of the “eyes.” Are they opposite or
alternate ? Examine them closely with the magnifying glass
and then with the lowest power of the microscope. What
do they appear to be ?
B. If the potato is a stem, it may branch; look over a lot of
potatoes to try to find a branching specimen. If such a one
is secured, sketch it.
1 Hydrangea Hortensia.
_ ? Examination of a lot of potatoes will usually discover specimens with an
inch or more of attached stem.
MAM.
TUBERS AND BULBS 47
C. Note the little scale overhanging the edge of the eye, and
see if you can ascertain what this scale represents.
D. Cut the potato across, and notice the faint broken line
which forms a sort of oval figure some distance inside
the skin. Place the cut surface in eosin solution, allow the
potato to stand so for many hours, and then examine, by
slicing off pieces parallel to the cut surface, to see how far
and into what portions the solution has penetrated. Refer
to the notes on the study of the parsnip (Sec. 21), and see
how far the behavior of the potato treated with eosin solu-
tion agrees with that of the parsnip so treated.
E. Cut a thin section at right angles to the skin, and examine
with a high power. Moisten the section with iodine solution
and examine again.
F. If possible, secure a potato which has been sprouting in a
warm place for a month or more (the longer the better), and
look near the origins of the sprouts for evidences of the loss
of material from the tuber.
EXPERIMENT XXIV
Use of cork.* * Carefully weigh a potato; then pare another
larger one, and cut portions from it until its weight is made
approximately equal to that of the first one. Expose both freely
to the air for some days and reweigh. What does the result show
in regard to the use of the corky layer of the epidermis?
34. Structure of a bulb; the onion.
A. Examine the external appearance of the onion, and observe
the thin membranaceous skin which covers it. This skin
consists of the broad sheathing bases of the outer leaves
which grew on the onion plant during the summer. Remove
these and notice the thick scales (also formed from bases of
leaves) which make up the substance of the bulb.
B. Make a transverse section of the onion at about the middle,
and sketch the rings of which it is composed. Cut a thin
48 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
section from the interior of the bulb, examine with a mod-
erate power of the microscope, and note the thin-walled cells
of which it is composed.
C. Split another onion from top to bottom and try to find:
1. The broad flattened stem inside at the base.
2. The central bud.
3. The bulb scales.
4. In some onions (particularly in large, irregular ones) the
bulblets, or side bulbs, arising in the axes of the scales
near the base.
D. Test the cut surfaces for starch.
EXPERIMENT XXV
Testing for reserve sugar in an onion. Boil some slices of onion in a little
water and filter the latter through a paper filter to remove bits of the bulb
that may be left in it. Add a little Fehling’s solution to the liquid thus
obtained and heat to boiling. Result?! What is proved ?
EXPERIMENT XXVI
Testing an onion for proteids. Heat a rather thick slice of onion in a por-
celain evaporating dish with a little strong nitric acid until the latter just
begins to boil.2 Pour off the excess of acid, rinse the portion of onion for
a moment with water, and add enough ammonia to cover it. Note any
color changes. What is proved ? =
BUDS
X35. Dissection of the horse-chestnut bud. ** Examine one of
the lateral buds on a twig in its winter or early spring condition.
A. Make a sketch of the external appearance of the bud as
seen with a lens. How are the scales arranged ? Notice th
sticky coating upon them,
1 The mixture usually blackens at length, probably owing to the presence of
sulphur in the onion. .
2 Do not allow the acid to touch the hands or the clothing. 3
3 Buds of buckeye, maple, or box elder will answer, but not as well. They may 4 -
be forced to open early by placing twigs in water in a warm room for several weeks.
DISSECTION OF A WINTER BUD 49
B. Remove the scales in pairs, arranging them thus:
1
oO
bo
A
6 6 4 2
1
How many pairs are found ?
As the scales are removed observe whether the sticky coat-
ing is thicker on the outside or the inside of each scale, and
whether it is equally abundant on all the successive pairs.
What do you suppose to be the probable use of this coating ?
Note the delicate veining of some of the scales as seen
through the magnifying glass. What does this mean ?
Inside the innermost pair are found two forked, woolly
objects. What are these? Their shape could be more
readily observed if the woolly coating were removed. Can
you suggest a use for the woolly coating ?
C. Examine a terminal bud in the same way in which you
have just studied the lateral bud. It may contain parts
not found in the other. What is the appearance of these
parts? What do they represent? If there is any doubt
about their nature, study them further on a horse-chestnut
tree during and immediately after the process of leafing
out in spring, or let the twigs remain in water for a few
weeks until the buds open.
50 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
D. For comparison study at least one of the following kinds
of buds in their winter or early spring condition: hickory,
butternut, beech, ash, magnolia (or tulip tree), lilac, balm of
Gilead, cottonwood, cultivated cherry.’
REFERENCE. Ganong, 7.
36. Study of a cabbage (a naked bud). Examine and sketch a
rather small, firm cabbage, preferably a red one, which has been
split lengthwise through the center, and note:
A. The short, thick, conical stem.
B. The crowded leaves which arise from the stem, the lower
and outer ones largest and most mature, the upper and inner-
most ones the smallest of the series.
C. The axillary buds, found in the angles made by some leaves
with the stem.
87. Study of vernation. Procure a considerable number of buds which are
just about to burst, and others which have begun to open. Cut each across
with a razor or very sharp scalpel ; examine first with a magnifying glass,
and then with the lowest power of the microscope. Make a careful sketch
of one section. Pick to pieces other buds of the same kinds under the
magnifying glass, and report upon the manner in which the leaves are
packed away.
REFERENCE. Kerner-Oliver, 2.
38. The growing apex of the stem. The tip of the stem consists of tissue
which is undergoing (or in resting buds is ready to undergo) rapid cell divi-
sion, thus continuing the growth of the stem. The structure of this region
in dicotyledons is difficult to make out and it is not recommended that
beginners should undertake to study it.
Hippuris.? Choose a stem with a strong terminal bud, and trim away
from near the tip all the larger leaves. Cut off about a third of an inch of
the tip of the stem, hold it point downward between the thumb and fore-
finger, and try to get a smooth longitudinal section through the axis of the
bud. If the latter is first split into halves and then successive sections are
cut from each half, some one may be found to have passed exactly through
1 If some of the buds are studied at home, pupils will have a better chance to
pene at leisure the unfolding process.
ippuris is not available, Myriophyllum, which grows readily in aquaria
the year round, may be substituted, RE i A J d
LEAVES 51
the middle of the bud.! The cell contents may, in great part, be removed,
and the sections rendered more transparent by treating them for some time
with strong potash solution, which is then to be washed out, and the sections
placed in concentrated acetic acid. They may be examined in acetic acid or
in a solution of potassium acetate.
Examine the sections with a power of 200-800 diameters and make out
` the way in which the growing apex of the stem is capped by a series of
layers of cells as follows :
A. On the outside a single layer, the dermatogen, from which the epi-
dermis is developed.
B. Beneath this the periblem, four layers of cells from which the bark, or
cortex, is formed.
C. Within the layers of the periblem, the plerome, out of which the axial
fibro-vascular bundle of the stem is for the most part formed.
Make a drawing to show the relations of all the parts above described, and
(lower down on the stem) the origins of the leaves.
LEAVES
39. The elm leaf.” * *
A. Sketch the leafy twig of elm that is supplied to you.
Report on the following points :
1. How many rows of leaves ?
2. How much overlapping of leaves when the twig is held
with the upper sides of the leaves toward you? What
would be the advantages or disadvantages of much over-
lapping? Are the spaces between the edges of the leaves
large or small compared with the leaves themselves ?
B. Pull off a single leaf and make a sketch of its under sur-
face, about natural size. Label the broad part the blade, the
stalk by which it is attached to the twig leafstalk or petiole,
the appendages at its base stipules. Study the outline of the
leaf and answer these questions (see Principles, Appendix) :
1. What is the shape of the leaf as a whole ?
1 Unless the students have had considerable practice in making sections it will
be better to purchase slides of microtome sections of some growing point.
2 If this subject is taken up during the winter, it will be necessary to use gera-
nium or other leaves from the florists for the study of leaf anatomy, and potted
geraniums, begonias, lilies, etc., for leaf arrangement.
52 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
2. Is the leaf bilaterally symmetrical; i.e. is there a middle
line running through it lengthwise, along which it could
be so folded that the two sides would nearly coincide ?
3. Is the leaf dorsiventral; i.e., has it distinct upper and 7
under surfaces ?
4. Notice that the leaf is traversed lengthwise by a strong -
midrib and that many so-called veins run from this to
the margin. Are these veins parallel? Hold the leaf up
towards the light and see how the main veins are con-
nected by smaller veinlets. Examine with your glass the ©
leaf as held to the light, and make a careful sketch of
portions of one or two veins and the intersecting veinlets.
How is the course of the veins shown on the upper sur-
face of the leaf?
5. Examine both surfaces of the leaf with the glass and look
for hairs distributed on the surfaces. Describe the man-
ner in which the hairs are arranged.
40. The maple leaf.
A. Sketch the leafy twig.
1. How are the leaves arranged ?
2. How are the petioles distorted from their natural posi-
tions to bring the proper surface of the leaf upward toward
the light ?
3. Do the edges of these leaves show larger spaces between
them than the elm leaves did; i.e. would a spray of maple
intercept the sunlight more or less perfectly than a spray
of elm? Pull off a single leaf and sketch its lower sur-
face, about natural size.
4, Of the two main parts (blade and petiole), which is more
developed in the maple than in the elm leaf ?
B. Describe :
1. The shape of the maple leaf as a whole. To settle this,
place the leaf on paper, mark the positions of the extreme
points, and connect these by a smooth line.
A
A me
LEAF MOVEMENTS AND LIGHT 53
2. Its outline as to main divisions. Of what kind and how
many ?
3. The detailed outline of the margin.
Compare the mode of veining, or venation, of the elm and
the maple leaf by making a diagram of each (see Principles,
Chapter X).
The leaves of elm and of maple agree in being netted veined,
i.e. in having veinlets that join each other at many angles, so as
to forma sort of delicate lace work.
Such a leaf as that of the elm is said to be feather veined, or
pinnately veined. The maple leaf, or any leaf with closely similar
venation, is said to be palmately veined. Describe the difference
between the two plans of venation.
LEAF ARRANGEMENT FOR EXPOSURE TO LIGHT
AND AIR; HELIOTROPIC MOVEMENTS OF
LEAVES AND SHOOTS
EXPERIMENT XXVII
Is the nocturnal position due to removal of the light stimulus or to other causes ?
Remove a pot containing an oxalis or a clover plant from a sunny window
to a dark closet, at about the same temperature, and note at intervals of
five minutes the condition of its leaves for half an hour or more,
REFERENCES. Darwin and Acton, 11; Pfeffer-Ewart, 31, III; Detmer-
Moor, 9.
EXPERIMENT XXVIII
Determination of the values of illumination to produce various leaf positions.! A
Select a few common bean plants (Phaseolus) growing vigorously in a sunny
place, or a locust tree (Robinia) at the time in the spring when its leaves
have just reached their full size.
A. Note and sketch the positions of the leaves as follows :
1. After dusk.
2. In cloudy daylight or near dusk.
8. In intense sunlight, near noon.
1 This is preferably an out-of-door study.
54 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
B. Determine the relative proportion of the maximum illumination of
sunlight needed to bring about positions 1, 2, and 3. The light meas-
urements are to be made by means of ordinary photographic printing
paper (‘‘solio”’? paper answers well) as follows: cut the paper in a
very dark room into pieces about an inch square and at once put them
into small pasteboard or tin boxes and shut them away in a close drawer
or a windowless closet. All the paper in each box must be cut from the
same sheet of sensitive paper. One square of paper may be marked with
a violet aniline pencil and then exposed, at about noon, to the rays
out of doors, so that they will strike it vertically. Note exactly with a
watch in how many seconds the pencil mark nearly disappears. The
paper should then be at once shut up in the box from which it was
taken. This darkened square of paper may now be used as a standard.
If it darkened in 30 seconds, and another square used to measure illu-
mination (1) darkened to the same tint in 2400 seconds, then illumina-
tion (1) was ,4 full sunlight, or 1.25 per cent.
RECORD
Highest illumination for position 1 ............
Average illumination for position 2 ............
Least illumination for position 3 ...........
What is the apparent object of these movements ? What other plants have
as many positions as the bean and the locust ?
REFERENCE, Pfeffer-Ewart, 31, III.
EXPERIMENT XXIX
Can growing leaves adapt their positions to new light relations ? * *
Select a young, leafy, vertical branch of maple growing out of
doors, or a vigorous young sunflower (Helianthus) plant growing
out of doors or under nearly vertical light. Bend the shoot into
a horizontal position and note whether the leaves adapt them-
selves to their new relations. If there is any adaptation, describe
exactly the leaf movements by which it is brought about.
REFERENCE. Pfeffer-Ewart, 31, III.
1 Less satisfactory studies can be made of geraniums, begonias, or other plants
grown in the window and turned at intervals of several wees:
MINUTE STRUCTURE OF LEAVES 55
EXPERIMENT XXX
How do young shoots of English ivy bend with reference to light? Place a
thrifty potted plant of English ivy before a small window, e.g. an ordinary
cellar window, or in a large covered box, painted dull black within and
open only on the side toward a south window. After some days note the
position of the tips of the shoots. Explain the use to the plant of their
movements.
REFERENCE. Detmer-Moor, 9.
41. Sun leaves and shade leaves. Select for study some species of shrub
or tree which furnishes a dense shade. Deciduous species will answer, but
broad-leafed evergreens, like hollies, some rhododendrons, or live oaks are
still better. Why ? Gather some of the outer leaves and some of the inner-
most ones from the same tree. Measure the per cent of total illumination
received by the innermost leaves, as described in Exp. XXVIII. Make a
detailed comparison of the two kinds of leaves (those grown in sun and in
shade) as follows :
A. Comparison of average areas (see Exp. XX XVIII).
B. Comparison of hairiness or scaliness of the under surfaces.
C. Comparison of thickness of leaves. Use a power of 25-50 diameters
and a micrometer eyepiece, if one is available.
D. Comparison of details of structure of cross sections (see Secs. 42, 43).
Explain as fully as possible all the differences noted in comparisons
A-D above.
REFERENCE. Clements, 59.
MINUTE STRUCTURE OF LEAVES; FUNCTIONS
OF LEAVES
42. Minute structure of lily leaf.” * *
A. The student should first examine with m.p. a cross section
of the leaf. This will show:
1. The upper epidermis of the leaf, a thin, nearly transpar-
ent membrane.
2. The intermediate tissues.
3. The lower epidermis.
1 A simpler study may be made by comparing the illuminations and structures
of characteristic sun plants and shade plants, for instance Portulaca, Sedum, etc.,
with Arisema, Aralia, Clintonia, Trillium, ete., each grown in its natural habitat.
2 Any kind of lily will answer. Other leaves are equally good but many of
them are not obtainable at all seasons. Some excellent kinds are Fuchsia, English
56 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
In order to ascertain the relations of the parts, and to get
their names, consult Principles, Fig. 112. Your section is by no
means exactly like the figure; sketch it. Label properly all the
parts shown in your sketch.
Are any differences noticeable between the upper and the lower
epidermis ? Between the layers of cells immediately adjacent to
each ? Test some sections with phloroglucin (Sec. 12, D).
B. Examine with a power of 200 or more diameters the outer
surface of a piece of epidermis from the lower side of the
leaf! Sketch carefully, comparing your sketch with Prin-
ciples, Fig. 113, and labeling it to agree with that figure.
C. Examine another piece from the upper surface; sketch it.
How does the number of stomata in the two cases compare ?
REFERENCE. Strasburger-Hillhouse, 6.
43. Study of the leaf of ‘t rubber plant ’’ (Ficus elastica).* *
A. Make preparations of the leaf of the so-called rubber plant
as already described for the lily leaf. Study and sketch them
and then compare the two types of leaf:
As regards thickness of epidermis.
As regards number of layers of cells in the epidermis.
As regards development of the palisade layers.
As regards amount of fibro-vascular material (veins).
As regards freedom of exposure of the stomata openings
to the air,
CU £0 A
ivy (Hedera), willow, maple, poplar (any species, as cottonwood, aspen, ete.), the
thicker-leaved species of aster, apple, pear, plum, quince, beet. Thin sections
may be cut free-hand, especially if the leaf is doubled together several times or
held between two bits of elder pith. If only a part of the section is very thin, it
will answer almost as well as if it were equally thin throughout. The sections
may be made much more transparent if they are soaked in potash solution until
most of the green color disappears, and then treated with acetic acid. Both
these sections and those in their natural condition should be examined. Some
sections in their natural condition should be treated with phloroglucin.
1 The epidermis may be started with a sharp scalpel and then peeled off with
small forceps and mounted in water for microscopical examination. The epidermis
of Ficus leaf (Sec. 43) will need to be pared off with a very sharp razor held par-
allel to the leaf surface. The stomata may be counted by use of an eyepiece
micrometer ruled in squares. Find how many divisions of the stage micrometer
equal one side of this square; then substitute a bit of epidermis for the stage
micrometer, and count the number of stomata in an eyepiece square. Calculate
the number of stomata in a leaf of the kind examined; also, if possible, the
number for the entire plant. i :
PHOTOSYNTHESIS ot
E. Let an entire leaf of each kind remain for some hours in a
warm, sunny place and notice the comparative amount of
wilting in both cases. Explain.
REFERENCES. Kerner-Oliver, 2; Haberlandt, 33; Schimper-
Fisher, 56; Warming-Graebner, 57.
EXPERIMENT XXXI
Oxygen making in sunlight.* * Place a green aquatic plant in
a glass jar full of water, at about 70° F. (21° C.), in front of a
sunny window.’ Note the formation of oxygen bubbles looking
silvery by reflected light.2 Remove to a dark closet and after
fifteen minutes examine by lamplight, to see whether the rise of
bubbles still continues. i
This gas may be shown to be oxygen by collecting some of it
in a small inverted test tube filled with water and thrusting
into it the glowing coal of a match just blown out. It is not,
however, always very easy to do this satisfactorily. - i
Repeat the experiment, using water which has been well
boiled and then quickly cooled in a tightly covered vessel.
Boiling removes all the dissolved gases from water (including
much carbon dioxide), and they are not redissolved in any
considerable quantity for many hours.
REFERENCES. Detmer-Moor, 9; Darwin and Acton, 11.
EXPERIMENT XXXII
Occurrence of starch in nasturtium leaves.* * Toward the close
of a very sunny day collect some bean leaves or leaves of nastur-
tium (Zropeolum). Boil these in water for a few minutes, to kill
the protoplasmic contents of the cells and to soften and swell
the starch grains. Soak the leaves, after boiling, in strong, hot
alcohol for half an hour, to dissolve out the chlorophyll, which
1 Elodea, Myriophyllum, Chrysosplenium, Potamogeton, any of the green
aquatic flowering plants, the aquatic moss, Fontinalis, or even the common pond
scum, Spirogyra, will do for this experiment.
2Some of the earlier bubbles may contain a good deal of air which was
dissolved in the water and set free as it grows warm, but the later bubbles will
be fairly pure oxygen. à
pri
58 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
might obscure the starch test. Heat the alcohol in a water bath
away from any flame. Place the leaves for ten or fifteen minutes
in a solution of iodine, rinse off with water, put in a white plate
or saucer, and note what portions of the leaf, if any, show the
presence of starch.
REFERENCES. Detmer-Moor, 9; Ganong, 10; Darwin and
Acton, 11; Pfeffer-Ewart, 31, I.
EXPERIMENT XXXII
Consumption of starch in nasturtium (Tropzolum) leaves.* *
Select some healthy leaves of Zropeolum on a plant growing
vigorously indoors, or, still better, in the open air. Shut off the
sunlight from parts of the selected
leaves (which are to be left on the
plant and as little injured as possible)
by pinning circular disks of cork
loosely on opposite sides of the leaf,
as shown in Fig. 3. On the afternoon
of the next day remove from the plant
= these leaves and (for control purposes)
Fie, 3. Leaf of Tropeolum some others to which no cork disks
partly covered with disks of were attached. Treat all as described
cork and exposed to sunlight . : y é
in the preceding experiment, taking
especial pains to get rid of the chlorophyll by changing the
alcohol as many times as may be necessary. What does this
experiment show in regard to the consumption of starch in the
leaf? What has caused its disappearance ? 1
It may be fairly taken for granted that if the leaf contained any
starch when the corks were pinned onto it, all parts of it were
somewhat equally full of starch. If the experiment results in
showing absence of starch in the part deprived of light by the
cork, it may be thought that starch manufacture was stopped
1 Or put a plant with starch in the leaves in a moist chamber without light
for a day or two, with cut-off leaves beside it. Then test the attached leaves and
the cut-off ones for starch. Explain results.
g
PHOTOSYNTHESIS 59
in that portion partly because of lack of light, and partly because
the supply of air (and therefore of carbon dioxide) was very
scanty under the cork. The truth of the supposition that lack of
carbon dioxide was responsible for the failure to make starch
may be tested by boring a large hole with a cork borer through
each cork before fastening it in place on the leaf, and cementing
over the hole a thin cover glass. Then some of the parts of the
leaf covered by the cork are lighted while others are not, and if
the lighted parts show starch, it was lack of light only that
prevented its formation in the shaded parts.
REFERENCES. (See Experiment XXXII.)
EXPERIMENT XXXIV
Can starch making go on when the stomata are shut off from all
air supply ? Select a thrifty potted plant of some species which
has thin leaves, with stomata only on the under surface (e.g. prim-
rose, begonia). Put the plant in an absolutely dark place for
twenty-four hours, and then coat half of the under surface of one
or more leaves with vaseline and expose the plant for a day to
‘bright sunlight. Wipe off most of the vaseline with cotton wool
and remove the rest by washing, with a swab or soft brush, in
several successive quantities of benzine.' Then boil, treat with
alcohol, and test for starch as directed in Exp. XXXII. Explain
the result.
REFERENCE. Ganong, 10.
EXPERIMENT XXXV
Can squash seedlings make chlorophyll in the dark?* * Plant
some squash seeds in sawdust or sand, and keep part of them in
a good light, while others are kept in total darkness at about the
same temperature. When the plumules of those in the light are
developed into half-grown leaves, sketch both lots of seedlings
1Do not attempt this in the same room with a flame, or a lighted lamp or
gas jet.
60 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
and describe the main differences in color, height, and thickness
of hypocotyl, and in the development of the cotyledons of those
grown in darkness and in the light.
What is the conclusion in regard to power to make chlorophyll ?
Leave both lots in sunlight for a day and test some cotyle-
dons of each set for starch. Leave both sets in sunlight for
several days more and note any changes in the appearance of
those which were started in darkness. Test the latter again for
starch. Conclusions ?
REFERENCE. Pfeffer-Ewart, 31, II.
EXPERIMENT XXXVI
Do leaves give off water? If so, from which surface is it given off
more abundantly? * * Fasten two small watch glasses, one on each
side of a leaf of a plant growing vigorously in a pot or out of doors.
Fic. 4. Watch glasses fastened on a leaf of Chinese primrose
Hydrangea,’ primrose, or cineraria? are good plants for the pur-
pose, although many others will answer. The watch glasses may
be held in place by a spring clip, as shown in Fig. 4. Seal the
margin of each glass all the way around by means of vaseline or
barely melted grafting wax. Leave the plant for half an hour or
more in a sunny place, and then look for drops of water inside
1 H. Hortensia. 2 Senecio cruentus.
TRANSPIRATION 61
of each watch glass. If none are visible, carefully cut off the leaf
and place it for a few minutes in a box with a piece of ice or
put it out of doors in a cold place. Report the results. Examine
the upper and lower epidermis with the microscope and explain
the results noted.
REFERENCE. Osterhout, 13.
EXPERIMENT XXXVI
Through which side of a leaf of Ficus elastica does transpiration occur? The
student may already have found (Sec. 43) that there are no stomata on
the upper surface of the Ficus leaf which he studied. That fact makes this
leaf an excellent one for the study of the relation of stomata to transpiration.
Take two large, sound Ficus leaves, cut off pretty close to the stem of the
plant. Slip over the cut end of the petiole of each leaf a piece’of small
rubber tubing, wire this on, leaving about half of it free, and then double the
free end over and wire tightly, so as to make the covering moisture proof.
Warm some vaseline or grafting wax until it is almost liquid, and spread a
thin layer of it smoothly over the upper surface of one leaf and the lower
surface of the other. Hang both up in a sunny place in the laboratory and
watch them for a month or more.
What difference in the appearance of the two leaves becomes evident ?
What does the experiment prove ?
REFERENCE. Darwin and Acton, 11.
EXPERIMENT XXXVIII
Amount of water lost by transpiration. * * Procurea thrifty hydrangea? and
a small plant of Ficus elastica,? each growing in a small flowerpot, and with
the number of square inches of leaf surface in the two plants not too widely
different. Calculate the area of the leaf surface for each plant by dividing
the surface of a piece of tracing cloth into a series of squares one half inch
on a side, holding an average leaf of each plant against this and counting
the number of squares and parts of squares covered by the leaf. This area,
multiplied by the number of leaves for each plant, will give approximately
the total evaporating surface for each.4
1 This is also true of many other leaves, as those of the oleander, the lilac, and
most begonias, and any of them may be used for the experiment.
2 The common species of the greenhouse, Hydrangea Hortensia.
3 Commonly known as India-rubber plant. 2
4The quickest and most accurate method of procedure is to defer calculating
the leaf area until the conclusion of the experiment, and then to cut off all the
62 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
Transfer each plant to a glass battery jar of suitable size. Cover the jar
with a piece of thin sheet lead, slit to admit the stem of the plant, invert
the jar, and seal the lead to the glass with a hot mixture of beeswax and
rosin. Seal up the slit and the opening about the stem with grafting wax.
A thistle tube, such as is used by chemists, is also to be inserted, as shown
in Fig. 5. The mouth of this may be
kept corked when the tube is not in
use for watering.
Water each plant moderately and
weigh the plants separately on a
balance that is sensitive to one-fifth
gram. Record the weights, allow the
plants to stand in a sunny, warm
room for twenty-four hours, and
reweigh.
Add to each plant just the amount
of water which is lost,? and continue
the experiment in the same manner
for several days, so as to ascertain, if
possible, the effect upon transpiration
of varying amounts of water in the
atmosphere.
Fic. 5. A hydrangea potted in a Calculate the average loss per 100
battery jar for Exp. XXXVIII square inches of leaf surface for each
plant throughout the whole course of
the experiment. Divide the greater loss by the lesser to find the ratio. Find
the ratio of each plant’s greatest loss per day to its least loss per day, and
by comparing these ratios decide which transpires more regularly.
Try the effect of supplying very little water to each, so that the hydran-
gea will begin to droop, and see whether this changes the relative amount of
transpiration for the two plants. Vary the conditions of the experiment for
a day or two as regards temperature, and again for a day or two as regards
light, and note the effect upon the amount of transpiration.
The structure of the Ficus (India-rubber plant) leaf has already been
studied. That of the hydrangea is looser in texture and more like the leaf
of the lily.
leaves, make blue prints of them, cut these out, and weigh them. The total area
may easily be calculated by comparison of the weight obtained with that of a
known area of the paper used.
1 It will be much more convenient to tie the hydrangea, if one has been chosen
that has but a single main stem. Instead of the hydrangea the common cineraria,
Senecio cruentus, or a small sunflower plant does very well.
2 The addition of known amounts of water may be made most conveniently by
measuring in a cylindrical graduate.
a
RISE OF WATER 63
What light does the structure throw on the results of the preceding
experiment ?
REFERENCES. Detmer-Moor, 9; Ganong, 10.
EXPERIMENT XXXIX
Passage of water from stem to leaf. Place a freshly cut leafy
shoot of some plant with large, thin leaves, such as Hydrangea
Hortensia, in eosin solution for a few minutes. As soon as the
leaves show a decided reddening pull some of them off and
sketch the red stains on the scars thus made. What does this
show ?
EXPERIMENT XL
Rise of water in leaves.* * Put the freshly cut ends of the
petioles of several thin leaves of different kinds into small glasses,
each containing eosin solution to the depth of one quarter inch or
more. Allow them to stand for half an hour, and examine them
by holding up to the light and looking through them to see into
what parts the eosin solution has risen. Allow some of the leaves
to remain as much as twelve hours, and examine them again.
The red-stained portions of the leaf mark the lines along which,
under natural conditions, water rises into it. Cut across (near the
petiole or midrib ends) all the principal veins of some kind of
large, thin leaf. Then cut off the petiole and at once stand the
cut end, to which the blade is attached, in eosin solution. Repeat
with another leaf and stand in water. What do the results teach?
EXPERIMENT XLI
Does the leaf vary inits starch contents at different seasons? Collect in
early summer, at the close of a sunny day, some leaves of different kinds of
trees and shrubs and preserve them in alcohol. Collect other leaves of
the species as they are beginning to drop from the trees in autumn and pre-
serve them in the same way. Test some of each lot for starch, as described
in Exp. XXXII.
What does the result indicate ?
64 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
THE FLOWER OF THE HIGHER SEED PLANTS
44. The flower of the Trillium.* * *
A. Cut off the flower stalk rather close to the flower; stand the
latter, face down, on the table, and draw the parts then
shown. Label the green leaf-like parts sepals, and the white
parts, which alternate with these, petals.
B. Turn the flower face up and make another sketch, label-
ing the parts as before, together with the enlarged yellow ex-
tremities, or unthers, of the stalked organs called stamens.
C. Note and describe the way in which the petals alternate
with the sepals. Observe the arrangement of the edges of
the petals toward the base, how many with both edges
outside the others, how many with both edges inside, how
many with one edge in and one out.
Note the veining of both sepals and petals, observing in
which set they are more distinct.?
D. Pull off a sepal and make a sketch of it, natural size; then
remove a petal, flatten it out, and sketch it, natural size.)
E. Observe that the flower stalk is enlarged slightly at the
upper end into a rounded portion, the receptacle, on which
all the parts of the flower rest.
F. Note how the six stamens arise from the receptacle,
and their relations to the origins of the petals. Remove the
remaining petals (cutting them off near the bottom with a
1 Only one flower need be studied to give an idea of the floral organs ordinarily
found. More advanced studies are suggested at the end of Part III. ;
If none of the three flowers here described can be had, the instructor can
readily frame a set of directions for the examination of some other form. Among
the simplest types which can readily be grown in the greenhouse for class study
are Sedum acre and Crassula quadrifida. Matthiola is not quite so simple, but
the single-flowered varieties answer very well. Scilla sibirica is often available.
Another convenient greenhouse flower is the Roman hyacinth.
2 In flowers with delicate white petals the distribution of the fibro-vascular
bundles can usually be readily shown by standing the freshly cut end of the
flower stalk in eosin for a short time, until colored veins begin to appear in the
petals. The experiment succeeds readily with apple, cherry, or plum blossoms; with
white gillyflower the coloration is very prompt. Lily of the valley is perhaps as
interesting a flower as any on which to try the experiment, since the well-defined
stained stripes are separated by portions quite free from stain, and the pistils
are also colored.
3
t
t
FLOWER OF TRILLIUM 65
knife), and sketch the stamens, together with the other
structure, the pistil, which stands in the center.
Cut off one stamen, and sketch it as seen through the lens.
Notice that it consists of a greenish stalk, the filament, and
a broader portion, the anther. The latter is easily seen to
contain a prolongation of the green filament, nearly sur-
rounded by a yellow substance. In the bud it will be found
that the anther consists of four long pouches, or pollen cham-
bers, which are attached by their whole length to the fila-
ment. When the flower is fairly open the pollen chambers
of each pair have already split down their margins, thus
appearing as one on each side, and are discharging a yellow,
somewhat sticky powder, the pollen. x
Examine one of the anthers with a lens and sketch it.
Cut thin cross sections of an immature anther and draw
under l.p., showing the pollen chambers.
G. Cut away allthe stamens and sketch the pistil. It consistsof a
stout lower portion, the ovule case, or ovary, which is six-ridged
or angled, and which bears at its summit three slender stigmas.
In another flower, which has begun to wither (and in which
the ovary is larger than in a newly opened flower), cut the
ovary across about the middle, and with the lens determine
the number of chambers, or locules, which it contains. Exam-
ine the cross section with the lens; sketch it, and note par-
ticularly the appearance and mode ‘of attachment of the
‘undeveloped seeds, or ovules, with which it is filled. Make a
vertical section of another rather mature ovary, and examine
this in the same way.
H. Using a fresh flower, construct a diagram to show the rela-
tion of the parts on an imaginary cross section. Construct .
a diagram of a longitudinal section of the flower, showing
the contents of the ovary.
1 It is important to notice that such a diagram is not a picture of the section
actually produced by cutting through the flower crosswise at any one level, but
that it is rather a projection of the sections through the most typical part of each
of the floral organs (see Principles, Fig. 138).
66
STRUCTURE AND PHYSIOLOGY OF.SEED PLANTS
Make a tabular list of the parts of the flower, beginning
with the sepals, giving the order of parts and the number in
each set.
45. The flower of the tulip.
A. Make a sketch of a side view of the well-opened flower as it appears
E.
when standing in sunlight. Observe that there is a set of outer flower
leaves and a set of inner ones.? Label the outer set sepals and the inner
set petals. In most flowers the parts of the outer set are greenish, and
those of the inner set of some other color. Itis often convenient to
use the name perianth (meaning around the flower) for the two sets
taken together. Note the white waxy bloom on the exterior surface
of the outer segments of the perianth. What is the use of this ? Observe
the manner in which the inner segments of the perianth arise from the
top of the flower stalk and their relation to the points of attachment of
the outer segments. Ina flower not too widely opened note the relative
position of the inner segments of the perianth, how many wholly outside
the other two, how many wholly inside, how many with .one edge in
and one edge out.
. Remove one of the sepals by cutting it off close to its attachment to
the peduncle, and examine the veining by holding it up in a strong
light and looking through it. Make a sketch to show the general out-
line and the shape of the tip.
. Examine a petal in the same way, and sketch it.
. Cut off the remaining portions of the perianth, leaving about a quarter
of an inch at the base of each segment. Sketch the upright, triangular,
pillar-like structure in the center,—label it pistil; sketch the organs
which spring from around its base, and label these stamens:
Note the fact that each stamen arises from a point just above and
within the base of a segment of the perianth. Each stamen consists of
a somewhat conical or awl-shaped portion below, the filament, sur-
mounted by an ovate-linear portion, the anther.
Sketch one of the stamens about twice natural size and label it x 2.
Is the attachment of the anther to the filament such as to admit of
any nodding or twisting movement of the former? In a young flower
note the tubular pouches, or pollen chambers, of which the anther is
composed, and the slits by which these open. Observe the dark-colored
pollen which escapes from the anther cells and adheres to paper or to
the fingers. Examine a newly opened anther with the lens and sketch
it. Cut thin cross sections of an unopened anther and examine with l.p.
Note that there are four pollen chambers, two on each side.
1 Tulipa gesneriana. 2 Best seen in a flower which is just opening.
a a
dys
H.
FLOWER OF BUTTERCUP 67
Cut away all the stamens and note the two portions of the pistil, —
the ovule case, or ovary, below, and above three roughened, scroll-like
lobes of the stigma. Make a sketch of these parts about twice natural
size, and label them x 2. Touch a small camel’s-hair brush to one of
the anthers and then transfer the pollen thus removed to the stigma.
This operation is merely an imitation of the work done by insects which
visit the flowers out of doors. Does the pollen cling readily to the
rough stigmatic surface ? Examine this adhering pollen under l.p. and
sketch a few grains of it, together with the bit of the stigma to which
it clings. Make a cross section of the ovary about midway of its
length, and sketch the section as seen through the lens. Label the
three chambers shown locules, and the white, egg-shaped objects within
ovules.1
Make a longitudinal section of another ovary, taking pains to secure
a good view of the ovules, and sketch as seen through the lens,
. Making use of the information already gained and the cross section of
the ovary as sketched, construct a diagram of a cross section of the
entire flower, showing the contents of the ovary.
Split a flower lengthwise and construct a longitudinal section of the
entire flower.
46. The flower of the buttercup.* *
A.
B.
C.
Sketch the mature flower as seen in a side view, looking a
little down into it. Label the pale greenish-yellow, hairy
outermost parts, sepals; the larger, bright yellow parts above
and within these, petals; and the yellow-knobbed organs which
occupy a good deal of the interior of the flower, stamens.
Note the difference in the position of the sepals of a newly
opened flower and that of the sepals of a flower which has
opened as widely as possible. Note the way in which the
petals are arranged in relation to the sepals. In an opening
flower observe the arrangement of the edges of the petals, —
how many entirely outside the others, how many entirely
inside, how many with one edge in and the other out.
Cut off a sepal and a petal, each close to its attachment to
the flower; place both, face down, on a sheet of paper, and
1 The section will be more satisfactory if made from an older flower, grown out
-= of doors, from which the perianth has fallen. In this case label the contained
objects developing seeds.
68 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
sketch about twice the natural size and label it x 2. Describe
the difference in appearance between the outer and the inner
surface of the sepal and of the petal. Note the little scale
at the base of the petal, inside. Lift up the free edge of this
scale with the point of a needle and look for nectar.
D. Strip off all the parts from a flower which has lost its
petals, until nothing is left but a slender, conical object a
little more than an eighth of an inch in length. This is
the receptacle or summit of the flower stalk.
E. In a fully opened flower note the numerous yellow-tipped
stamens, each consisting of a short stalk, the filament, and
an enlarged yellow knob at the end, the anther. Note the
division of the anther into two portions, which appear from
the outside as parallel ridges, but which are really closed
cavities full of pollen.
F. Observe in the interior of the flower the somewhat globular
mass (in a young flower almost covered by the stamens).
This is a group of pistils. Study one of these groups in a
flower from which the stamens have mostly fallen off, and
make an enlarged sketch of the head of pistils. Remove
some of the pistils from a mature head, and sketch a single
one as seen with the magnifying glass. Label the little
knob or beak at the upper end of the pistil stigma, and the
main body of the pistil the ovary. Make a section of one of
the pistils, parallel to the flattened surfaces, and note the
partially matured seed within.
POLLINATION AND FERTILIZATION
EXPERIMENT XLII
Production of pollen tubes.* * Make a hanging-drop culture
(Sec. 204), or place a few drops of suitably diluted sirup of cane
sugar (Sec. 170), with some fresh pollen, in a concave cell ground
in a microscope slide, and cover with a thin glass circle. Place
the slide under a bell glass, with a wet cloth or sponge, to prevent __
THE BEAN POD 69
evaporation of the water, and set aside in a warm place, or merely
put some pollen in sirup in a watch crystal under the bell glass.
Examine from time to time to note the appearance of the pollen
tubes. Try several kinds of pollen if possible, using solutions of
various strengths. The following kinds of pollen form tubes
readily in sirups of the strengths indicated :
SLADE NOS 5 oe ve dP At cdr a a T a 1 to 3 per cent
DSIRE EDIE’ “alg, all ae ee 3 to 5 per cent
Cytisus canariensis (called Genista by florists) 15 per cent
OID INE Sa DUM TOSCO ee hey tej tied s 10 per cent
SWwech DOL wes hy ic et LO toloopercent
ATODOL set whe 2 S cI ee elec 15 per cent!
REFERENCE. Strasburger-Hillhouse, 6
THE FRUIT?
47. A capsule (legume), the bean pod.” * *
A. Lay the pod flat on the table and make a sketch of it, about
natural size. Label stigma, style, ovary, calyx, flower stalk.
B. Make a longitudinal section of the pod, at right angles to
the plane in which it lay as first sketched, and note the par-
tially developed seeds, the cavities in which they lie, and
the solid portion of the pod between each bean and the next.
m Split another pod, so as to leave all the beans lying undis-
turbed on one half of it, and sketch that half, showing the
beans lying in their natural position and the funiculus, or
stalk, by which each is attached to the placenta.
C. Make a cross section of another pod through one of the
- _ beans, sketch the section, and label the placenta. Break off
f sections of the pod and determine, by observing where the
1 The sweet-pea pollen and that of Tropæolum are easier to manage than any
other kinds of which the authors haye personal knowledge. If a concave slide is
not available, the cover glass may be propped up on bits of the thinnest broken
cover glasses. From presence of air or for some other reason, the formation of
pollen tubes often proceeds most rapidly just inside the margin of the cover glass.
2 Tf time is not available for all of these studies, two or three types will suffice.
8 Material in preservative fluid such as formalin will answer, or fresh string
beans or shell beans may be used.
70 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
most stringy portions are found, where the fibro-vascular
bundles are most numerous.
D. Examine some ripe pods of the preceding year,’ and notice
where the dehiscence, or splitting open of the pods, occurs,
whether down the placental edge, ventral suture, the other
edge, dorsal suture, or both.
48. A schizocarp, the fruit of caraway.” Examine a complete fruit,
“caraway seed” (magnified). If it has not been roughly handled,
it should show the remains of the stigmas, surmounting the two
halves, mericarps, of the fruit. The mericarps are borne on a
forked stalk, from which they remain suspended until blown
away by the wind or otherwise detached. Make a cross section
of one mericarp (if dry, after soaking it for a minute or two in
hot water). Draw it magnified and label the pericarp, with its
oil tubes and the seed within. The tubes contain the volatile oil
which gives the fruit its characteristic smell and flavor.
This fruit has no very effective means for securing dispersal.
Compare it in this respect with the fruits (commonly called
seeds) of parsnip and of carrot.
49. An akene, the fruit of dock.
A. Hold in the forceps a ripe fruit of any of the common kinds of dock,
and examine with the lens. Note the three dry, veiny, membranaceous
sepals by which the fruit is inclosed. On the outside of one or more
of the sepals is found a tubercle, or thickened appendage, which looks
like a little seed or grain. Cut off the tubercles from several of the
fruits; put these, with some uninjured ones, to float in a pan of water,
and watch their behavior for several hours. What is apparently the
use of the tubercle ?
Of what use are the sepals after drying up? Why do the fruits
cling to the plant long after ripening ?
B. Carefully remove the sepals and examine the fruit within them. What
is its color, size, and shape? Note the three tufted stigmas attached
by slender threads to the apex of the fruit. What does their tufted
shape indicate ?
What evidence is there that this seed-like fruit is not really a seed ?
1 Preserved dry for the purpose.
2 “Caraway seeds” can be bought from the druggists.
THE LEMON 71
C. Make a cross section of a fruit and notice whether the wall of the
ovary can be seen distinct from the seed coats. Compare the dock
fruit in this respect with the fruit of the buttercup shown in Prin-
ciples, Fig. 161. Such a fruit as either of these is called an akene.
50. A nut, the acorn.
A. Sketch the entire acorn, side view, with, the base inclosed in its invo-
lucre, the ‘‘ acorn cup.’ Note the remains of the stigma at the top of
the acorn.
B. Cut a cross section of the acorn about midway of its length. Note
the hard pericarp and the seed, with thick cotyledons.
C. Make a drawing of a lengthwise section of the seed cut at right angles
to the surfaces where the cotyledons join. Look for the plumule
and the hypocotyl. Note and describe the testa. Test the cotyledons
for starch and for oil, Note the taste of the seeds. How are they
disseminated ?
If possible, compare the acorn with such other nuts as the chest-
nut and the hazelnut.
51. A berry, the tomato.
A, Study the external form of the tomato, and note the persistent calyx
and peduncle.
B. Cut a cross section at about the middle of the tomato. Note the
thickness of the epidermis (peel off a strip) and of the wall of the ovary.
Note the number, size, form, and contents of the cells of the ovary.
Observe the thickness and texture of the partitions between the cells.
Sketch. What changes in the fruit of the pepper (Principles, Fig. 166)
would make it resemble a tomato ? Note the attachments of the seeds
to the placentas, and the gelatinous, slippery coating of each seed.
The tomato is a typical berry, but its structure presents fewer
points of interest than are found in some other fruits of the same
general character, so the student will do well to spend a little more
time on the examination of such fruits as the orange or the lemon.
52. A leathery-skinned berry, or hesperidium, the lemon. ** Pro-
cure a large lemon which is not withered ; if possible, one which
still shows the remains of the calyx at the base of the fruit.
A. Note the color, general shape, surface, remains of the calyx,
knob at portion formerly occupied by the stigma. Sketch
the fruit about natural size.
` B. Examine the pitted surface of the rind with the lens, and
sketch it,
aa
72 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
C. Remove the bit of stem and dried-up calyx from the base
of the fruit ; observe, above the calyx, the disk on which
the pistil stood. Note with the lens and count the minute
whitish, raised knobs at the bottom of the saucer-shaped
depression left by the removal of the disk. What are they ?
D. Make a transverse section of the lemon, not more than a
fifth of the way down from the stigma end, and note :
1. The thick skin, pale yellow near the outside, white within.
2. The more or less wedge-shaped divisions containing the
juicy pulp of the fruit. These are the matured locules of
the ovary ; count these.
3. The thin partition between the cells.
4. The central column or axis of white pithy tissue.
5. The location and attachment of any seeds that may be
in the section.
Make a sketch to illustrate these points.
E. Study the section with the lens and note the little spherical
reservoirs near the outer part of the skin, which contain the
oil of lemon which gives to lemon peel its characteristic smell
and taste.. With the razor cut a thin slice from the surface
of a lemon peel, some distance below the section, and at once
examine the freshly cut surface with a lens to see the reser-
voirs, still containing oil,—which, however, soon evapo-
rates. On the cut surface of the pulp (in the original cross
section) note the tubes or sacs in which the juice is contained.
These tubes are not cells, but their walls are built of cells.
F. Cut a fresh section across the lemon, about midway of its
length, and sketch it, bringing out the same points which s
were shown in the previous one. The fact that-the number
of ovary locules in the fruit corresponds with the number of ;
minute knobs in the depression at its base is due to the fact
that these knobs mark the points at which fibro-vascular
bundles passed from the flower stalk into the cells of the fruit,
carrying the sap by which the growth of the latter was
maintained.
; ee
—— a
STUDIES OF FRUITS Ta
Note the toughness and thickness of the seed coats. Taste
the kernel of the seed.
G. Cut a very thin slice from the surface of the skin, mount
in water, and examine with a medium power of the micro-
scope. Sketch the cellular structure shown, and compare it
with the sketch of the cork of the potato tuber.
Of what use to the fruit is a corky layer in the skin?
REFERENCE. Strasburger-Hillhouse, 6.
53. A drupe, the cherry. Make a cross section of a partly grown cherry, in
which the stone has not become too hard to cut. Make a magnified sketch
of it, showing the double pericarp, consisting of the exocarp, or fleshy part,
covered with a thin, tough epidermis, and the endocarp, or stone, containing
the seed. Crack some ripe cherry stones and study the seeds, à
If possible, compare with the structure of the cherry that of other drupes,
such as the peach, the fruit of the cocoanut (with the husk), the entire
fruit (with husk) of walnut, butternut, or hickory nut, and the fruit of the
Cornus, or dogwood.
54. An accessory fruit, the strawberry.
A. Study the flower of a strawberry, noting particularly the number,
shape, and position of the pistils.
B. Examine a series of strawberry fruits,1 beginning at the time when
the cluster of pistils shows signs of enlarging. How much does each
pistil enlarge ? What causes the increased size of the fruit ?
C. Study a firm, ripe strawberry with the lens, and draw the ripened
pistils, called akenes.
D. Cut a lengthwise section of the fruit and sketch it.
What is the main difference in proportions between a head of akenes, like
that in Principles, Fig. 161, and a strawberry ? What is the use of the
pulpiness of the ripened receptacle ?
55. Development of a fruit. Secure a series of as many stages as possible
in the development of some convenient fruit, as the common bean, from the
newly fertilized pistil to the full-grown pod.”
A. Make drawings of the entire fruit, the earlier stages x 4 or x 5, but .
all the later ones natural size.
B. Cut thin cross sections and lengthwise sections (through the seed) of
a series of fruits and sketch them, using a magnification of about 20
1 Material preserved in alcohol will answer. n
2 Other leguminous fruits, or any moderately large capsules or berries, will an-
= swer. Material in preservative fluid suffices for all but the study of the course of
absorbed liquids.
74
REFERENCE. Strasburger-Hillhouse, 6.
STRUCTURE AND PHYSIOLOGY OF SEED PLANTS
diameters for the earliest ones and ten or less for the later ones. Some
of the sections may be treated to advantage with potash solution and
acetic acid (Sec. 169). Note the changes in size and shape of the seed,
in relative development of seed coat and embryo, and in relative bulk
of the style, stigma, and ovary wall (pod) compared with the contained
seeds, as the latter mature. After treatment with potash, several steps
in the development of the embryo can be made out with m.p. Note
that when the developing seed is not more than 4 to 4 the length of the
mature (dry) seed, its interior is mainly embryo sac, with a rudimen-
tary embryo at one end. Make several drawings to show stages in the
process by which the embryo grows until it fills the sac.
. If fresh material can be had, cut off under water the stalk to which
some well-grown pods are attached. Transfer the stalk (without
exposing the newly cut surface to the air) into eosin solution and allow
it to stand for an hour or more in a warm, sunny place. Cut trans-
verse and longitudinal sections of the pods as soon as they appear well
stained along the edges, and slice off thin layers from the flat surface
of a pod. Sketch the distribution of the fibro-vascular bundles (recog-
nized by the stain) in all the sections.
s
PART II
TYPE STUDIES PRECEDED BY THE STUDY
OF THE PLANT CELL
THE PLANT CELL, ITS STRUCTURE AND
REPRODUCTION
56. The cell structure of the Spirogyra filament (App. 6).*
A. Examine living material. What is its habit of growth,
floating or attached? What is its color? How does it feel
between the fingers? Note that it is made up of filaments,
or threads.
B. Mount two or three filaments in water under a cover glass.
Examine with l.p. (low power). Are the filaments branched ? /
Do they vary in thickness? Note the cross partitions that
divide the filament into parts called cells. Draw the outline
of a filament under l.p.
C. Study a filament under h.p. (high power). Do the cells
vary in length? How much? Select favorable cells and
focus on the cross partitions between them to determine
their geometrical form. What is the form of the entire
cell? Draw a group of two or three cells on a large scale,
noting :
1. The transparent cell walls bounding the filament and
forming the cross partitions.
* To THE InsTRUCTOR: The exercise outlined in Sec. 56 is an excellent one to
acquaint the student with the use of the compound microscope and the interpre-
tation of the geometrical form of structures by focusing up and down. If the
‘instrument has not been used before, the student may be made familiar with its
parts and their manipulation as described on pages 10-14, under the heading
“ The Construction and Use of the Compound Microscope.”
75
w
T6
TYPE STUDIES
2. The one or more green spiral bands extending around in
the interior of the cell just-under the cell wall. Focus on
the band above and below, following it around the cell.
D. Place a drop of salt solution (5 or 10 per cent) at the side of
the cover glass, and draw it under by means of a small piece
of filter paper applied against the opposite edge. Note the
contraction of a delicate membrane away from the cell wall,
so that the former immediately becomes apparent as a con-
tinuous membrane inclosing the green bandand other contents
of the cell. This membrane and its contents comprise the
living substance, or protoplasm, of the Spirogyra cell, and is
the living cell or protoplast; its structure will be taken up in
the next section. The cell wall is composed of cellulose which
is not protoplasmic in character, being formed by the proto-
plast and constituting a protective case around it.
57. The structure of the protoplast of Spirogyra.* *
A. Mount a slide of living Spirogyra as described in Sec. 56, B,
to study the protoplast. Note under h.p.:
1. That each green spiral band, called a chromatophore, con-
tains several denser structures termed pyrenoids.
2. A globular or elliptical structure, the nucleus, near the
center of the cell, held in position by delicate protoplasmic
strands which radiate outward to the cell walls. The out-
line of the nucleus will probably be clearer when the
material is stained with iodine, as described in B.
3. A delicate lining, or plasma membrane, next the cell wall
under which the chromatophore lies imbedded in a layer
of protoplasm. The plasma membrane was demonstrated
when the protoplast was drawn away from the cell wall
by the salt solution, as described in Sec. 56, D.
4. That the interior of the protoplast contains no solid or
semifluid substance, except possibly some minute granules,
and must consequently be either liquid or gas. Which 3
alternative is suggested by the experiment with the salt
solution (Sec. 56, D) ? Renee
CELL STRUCTURE OF SPIROGYRA (gi
Draw a large figure of a cell showing the cell walls, plasma
membrane, chromatophore with pyrenoids, nucleus held in
place by the radiating protoplasmic strands, and the large
space in the interior of the cell free from protoplasm.
B. Place a drop of iodine solution (Sec. 169) at the side of the
cover glass, and draw it under by means of a small piece of
filter paper applied against the opposite edge.
1. Note the coloration, or staining, of the protoplasmic struc-
tures. The nucleus usually stands out sharply, and should
be drawn if it was not clearly seen in the unstained living
cell described in A.
2. Draw a portion of the chromatophore showing a pyrenoid
under the highest magnification. There will probably
be found a circle of dark granules around the pyrenoid.
These are starch grains, manufactured by the chromato-
phore in the presence of sunlight, the process being called
photosynthesis.
C. Plasmolysis. The shrinking of the protoplast away from the
cell wall when the cell is bathed in adenser solution, as that of
salt (described in Sec. 56, D), is called plasmolysis. Plasmolysis
is accomplished by the withdrawal of water from the interior
of the protoplast through the permeable plasma membrane
and cell wall when there is a denser solution outside of the
cell. Such a movement of water through a permeable mem-
brane is due to osmosis (Principles, Sec. 48). The plasma
membrane of the protoplast is normally held against the
cell wall in the living cell by pressure from within, and that
condition is called cell turgor. The fluid within the proto-
plast is termed cell sap and is contained in cavities called
vacuoles. The cell sap of Spirogyra is in one large vacuole
occupying the central region of the cell, in which the nucleus
is swung like a hammock by radiating strands of proto-
plasm. If the facts and principles illustrated by plasmolysis
in Spirogyra are not clear, repeat the experiment outlined in
' Sec. 56, D.
78 TYPE STUDIES
D. Place some living Spirogyra in alcohol and after several hours
note the extraction of a green pigment, chlorophyll, from the
chromatophores in the filaments. What change in the color of
the filaments ? The alcohol may be evaporated by gentle heat
in a shallow dish, leaving the chlorophyll as a green residue.
58. Photosynthesis in Spirogyra.
A. Perform the experiment in photosynthesis outlined in Exp. XXXI,
using Spirogyra for the subject.
B. Place Spirogyra for a day or two in the dark and then test for starch
as described in Sec. 57, B,2. Return the material to sunlight, and after
several hours test again. Compare results.
59. Cell reproduction in Spirogyra. New cells arise in Spirogyra
either (1) by cell division or (2) by cell unions to form reproduc-
tive cells called zygospores or zygotes.
60. Cell division in Spirogyra. Search a slide of Spirogyra for
adjacent cells in the same filament considerably shorter than the
average size. Such a pair will probably be sister or daughter cells
formed by the division of a mother cell. The division of the
mother cell is preceded by the division of the nucleus, after
which a partition wall of cellulose is formed between the daughter
nuclei. Spirogyra is, however, not a favorable subject for the
study of nuclear and cell division (See. 65).
61. Cell unions to form zygospores in Spirogyra.* * At times
Spirogyra fruits.
A. If living material is available, note the frequent change
in color and occasional dirty appearance of the filaments.
Mount fruiting material (either living or preserved) teased
out well. Note:
1. That certain cells contain thick-walled oval or elliptical
structures densely filled with protoplasm and food material.
These are zygospores or zygotes.
2. That the zygospores are formed by the union or conjuga-
tion of cells. In some species of Spirogyra the cell unions
are between different filaments, in other species between
1 The terms fruit and fructification will be used in Part II in an untechnical
sense to designate various forms of reproductive organs and processes.
ZYGOSPORE FORMATION IN SPIROGYRA 12
adjacent cells of the same filament. If the conjugation is
between different filaments, are the zygospores all formed
on one side or are some formed in the cells of one filament
and some in the other ?
B. Find and draw a number of stages under h.p. illustrating
the history of the cell union or conjugation. Note:
1. That the union takes place through processes put out
from adjacent cells. These unite to form a connecting tube.
2. That the protoplast from one cell passes into the other
and fuses with its protoplast.
3. That the product of this cell union is a fusion protoplast,
which forms a heavy wall about itself, thus becoming a
well-protected reproductive cell or spore. Note the changed
appearance of the contents of the spore, and the presence
of food material. Test for starch.
Cell unions of this character are sexual processes. The cells
which unite are called gametes and their product is a sexually
formed fusion cell. The fusion cell in Spirogyra is called a zygo-
spore, or zyyote, because the gametes are similar. For this reason,
also, this type of sexual reproduction is called isogamy (meaning
similar gametes).
REFERENCE (on the plant cell). Principles, Chap. XVIII.
QueEstions.* Describe the cell structure of Spirogyra. What
part of it is living substance and what part of it is non-
living? Why are the cross walls in the filament flat planes ?
What would you expect to be the form of the wall at the
free end of a filament? How are new filaments of Spi-
rogyra formed? How do the filaments grow and is the
growth confined to any special region? What are the essen-
tial features in the formation of zygospores which define
it as a sexual process? What part does the zygospore play
* To THE InstRUCTOR: The sets of questions presented in connection with the
type studies of Part II are intended to bring before the student fundamental
principles in connection with his laboratory and field work, and his reading.
Written or oral exercises may be planned on them if desired.
a
80 TYPE STUDIES
—— N e
in the life history of the plant? How is it adapted for
its purposes? Construct a series of diagrams that will
outline the life history of Spirogyra. What are believed
to be some of the advantages to an organism in having a |
method of sexual reproduction ?
62. Cell structure of the moss leaf compared with Spirogyra.
A. Mount a moss leaf in water and draw a group of cells under h.p., and
show details of protoplasmic structure in one of them. Note:
1. That the chlorophyll is contained in numerous small, disk-shaped
bodies called chloroplasts. How are they distributed in the cell ? I
2. The multiplication of the chloroplasts by simple constriction. Draw
stages showing their division. l
B. Plasmolyze the cells with salt solution, and draw a group. Why do
adjacent cells have flat side walls ?
C. Stain with iodine.
1. Where are starch grains formed ? Draw.
2. Where does the nucleus lie ?
3. How much of the cell is filled with cell sap ?
63. The Amæba (App. 7). i
A. Gather with a pipette some of the slime at the bottom or scum on l
the top of a culture of Amæœæbæ. Search, under m.p., for transparent, l
naked cells which slowly change their outline by thrusting out some =
processes, pseudopodia, and withdrawing others.
B. Study under h.p. the changes in form of an Ameba as it slowly moves
along, making a series of outline sketches. Note the flow of the gran-
ular cytoplasm into the pseudopodia as they are formed. f
C. Draw diagrammatically an individual on a large scale, showing:
1. The plasma membrane, colorless and without granules.
2. The granular cytoplasm inclosed by the plasma membrane, fre-
quently containing food inclusions, as, for example, one-celled plants
such as diatoms and desmids. How would you expect this food to
be taken into the interior of the Ameba ?
3. A dense spherical nucleus (not always easily found),
4. Vacuoles which form, and later suddenly disappear, and consequently
are called contractile vacuoles.
D. The Ameba, as is generally the case with an animal cell, is a naked
protoplast. Compare with a typical plant cell. What does one have
that is lacking in the other ? What do both have in common ?
The Ameba reproduces by construction, a single individual thus forming
two similar daughter Amæbæ (see Principles, Fig. 167, B).
NUCLEAR AND CELL DIVISION 81
64. Circulation of protoplasm in the cell. Use Elodea, or Nitella, or stamen
hairs of Tradescantia.
A. Mount young leaves of Hlodea in water. Examine the simple cell
structure and find a favorable region for detailed study.
1, Note the position and form of the chloroplasts, the nucleus, the cyto-
plasm, comparing with previous studies on plant cells.
2. Study the circulation of protoplasm next the wall of the cell. Focus
on a chloroplast as it moves along, trace its path in a simple sketch
or diagram, and determine how long it takes to travel a certain
distance measured with the micrometer. Warm the slide gently.
What is the effect upon the rate of movement? Describe the
moyement carefully. Is the direction the same in all cells? Does
the substance of the plasma membrane move, or is it granular
cytoplasm under the membrane ?
B. Mount a portion of the stem of Nitella, including uninjured internodal
cells. Note the line called the neutral zone, free from chloroplasts,
which runs diagonally across the cell. The protoplasm on either side
of this line moves in opposite directions (see Principles, Sec. 230).
. Cut the stamens out of an opening flower or large bud of Tradescantia
and mount in water. The stamen hairs are chains of large and very
beautiful cells in which the nucleus and arrangement of the cytoplasm
may be seen with especial clearness. Are there chloroplasts present ?
What gives the peculiar reddish violet color to the cell?
Draw a cell on a large scale under h.p. and show the position of the
nucleus, and the moving streams of protoplasm, and indicate the
directions of the flow by arrows.
65. Nuclear and cell division in the root tip of an onion or other region of
growth (App. 8). The details of nuclear structure and nuclear division,
called mitosis, can only be studied in material carefully killed and hardened
to preserve the soft protoplasm as nearly as possible in its normal condition.
Thin seetions must be cut with an instrument called the microtome and these
stained to differentiate the protoplasmic structure (Sec. 211). One of the
best stains is a combination of safranin (red) and gentian violet (blue).
A. Examine sections under l.p. to determine the relation of regions or
tissues, and diagram the position of the root.cap, the undifferentiated
embryonic tissue at the growing point, and the beginnings of the differ-
entiation which appears back of the growing point.
B. Select a typical well-stained cell in the resting condition. Draw under
h.p. and note :
1. The nucleus with one or more deeply stained globules, each of which
is a nucleolus, or nucleole; a loose network containing chromatin ;
the nuclear membrane ; the nuclear cavity which contains nuclear sap.
82
2.
3.
TYPE STUDIES
The cytoplasm, granular in structure, probably containing one or
more vacuoles which were filled with cell sap.
The cell walls separating the protoplasts from one another.
C. Find a nucleus in the midst of division (metaphase of mitosis). Note:
1.
3.
That the chromatin has become organized into a number of rod-
shaped bodies, chromosomes, which are grouped in the center of the
cell, and that the nuclear membrane has disappeared. Draw.
. That the chromosomes are arranged in a plate, equatorial plate, be-
tween the poles of a spindle composed of delicate spindle fibers. Try
to count the chromosomes.
Search for evidence of a lengthwise division of the chromosomes
into daughter chromosomes. Draw.
. Find a cell in which the daughter chromosomes have separated into
two sets and are passing towards or have been gathered at the poles of
the spindle (anaphase of mitosis). Note:
Uk
The separation of the daughter chromosomes into two groups and
their passing to the poles of the spindle to form the daughter nuclet.
Try to count the chromosomes in each daughter group and compare
with the count at the equatorial plate. Draw.
. The persistence of the spindle between the groups of daughter
chromosomes.
. The appearance of a delicate plate across the spindle, finally reach-
ing the sides of the cell. This is the cell plate and marks the position
of the new cell wall which will be formed, dividing the mother cell
into two daughter cells, each with a nucleus. Draw.
. Find a later stage after the daughter nuclei have become organized as
resting nuclei and the cell division is completed.
. Study the beginnings of nuclear division (prophase of mitosis) before
the spindle is formed and the chromosomes are gathered at the equa-
torial plate (metaphase). Note :
n
2.
3.
That the loose chromatin network becomes a thread, spirem.
That this thread divides transversely into segments, which are the
chromosomes. Draw.
That the spindle is developed from accumulations of protoplasm
(kinoplasm) at two poles outside of the nuclear membrane, Draw.
66. Characteristics of some organic compounds found in plant cells.
Certain organic compounds will be met so frequently in cell
studies upon the lower plants that some of their characteristics
should be known. They fall into two great classes: (1) the carbo-
hydrates, composed of carbon, oxygen, and hydrogen, represented
EUGLENA 83
by starch, sugar, cellulose, oils, and fats; and (2) the proteids,
which contain nitrogen, sulphur, and in some cases phosphorus,
in addition to carbon, oxygen, and hydrogen. The principal tests
for these substances and some characteristics of their appearance
are given in Part I as follows: (1) starch, Sec. 12, A; (2) sugar,
Sec. 12, B; (3) cellulose, Sec. 12,C; (4) oils and fats, Sec. 12, E;
(5) proteids, Sec. 12, F.
THE FLAGELLATES, OR FLAGELLATA
67. Euglena (App. 9). Study its habits in a glass dish placed near a
window. Do the organisms congregate in any part of the dish? Why?
A. Mount in a drop of water and examine under l.p. Describe move-
ments. Under h.p. study cell structure. Note and draw :
1. The naked protoplast ; arrangement and form of the chloroplasts.
2. A red pigment spot at the forward end. Can you suggest its pos-
sible function with reference to the behavior of the organism
towards light ?
3. The structure of the forward end with a narrow, slit-like opening
leading into a cavity ; the position of a long, hair-like flagellum, or
cilium. These structures will probably become clearer after staining
l with iodine, as described in B.
B. Drain off as much water as possible from under the cover glass and
then place a drop of iodine solution at the side. It will slowly diffuse
through the water, killing and staining the Huglenw. Watch and de-
scribe the effect. Draw details of the forward end, showing the flagel-
` lum and the opening.
C. Study Euglena in the encysted condition, when the protoplast is sur-
rounded by a protective wall. Search for examples of cell division
while in this condition. Draw.
THE SLIME MOLDS, OR MYXOMYCETES
68. The spore fruit of a slime mold. The fructifications of the slime molds
are certainly plant-like and have been studied and classified chiefly by bot-
anists. Such typesas Stemonitis, Arcyria, Hemitrichia, and Lycogola are
favorable for study.
4 A. Draw a habit sketch of the spore fruit. Note:
r 1. The character of the attachment, whether or not stalked ; the spore
case.
84 TYPE STUDIES
2. The wall of the spore case. Has it a cellular structure ?
3. The thread- or net-like structure, capillitium, within the spore case
and the powdery spore mass.
B. Under h.p. draw a portion of the capillitium, showing markings, and a
group of spores.
69. The plasmodium. This stage in the life history, when available, may
be made the subject of very interesting studies on the structure and behavior
of protoplasm.
A. Mount a small portion and examine under low and high powers. Note
its consistence, structure, and contents. Describe and identify the food
contents as far as possible. Is starch present? Are oils or fats pres-
ent? Do you find any microscopic organisms which have been ingulfed
by the plasmodium?
B. Place the plasmodium on moist blotting paper under a bell glass.
Devise experiments to determine its reaction:
1. To bright illumination coming from one direction, with darkness
or faint illumination on the other side.
2. To warmth on one side.
3. To moisture on one side contrasted with dryness on the other.
C. Should the plasmodium begin to fructify, trace and describe the devel-
opment of the spore cases.
70. The flagellate-like stage of a slime mold. Try to germinate fresh spores
in a hanging drop (Sec. 204) or a covered watch glass. Use water in which
decaying wood has been soaked. Study the structure and habits of. the
motile protoplasts derived from the spores; also the amoeboid condition,
myxamoebee, which follows, and trace if possible the union of the myxa-
moebee to form a new plasmodium.
REFERENCE (to slime molds). Macbride, 38.
THE BLUE-GREEN ALG, OR CYANOPHYCEA
71. Field work on the blue-green alge. Good displays of the blue-green
alge may be found in open drains and stagnant pools which are somewhat
foul. Ditches and pools in salt marshes will furnish excellent material. —
Slimy, dark green growths on the surface of damp flowerpots, woodwork,
and earth are frequently composed of these growths. Water blooms are
generally made up of either blue-green alge or Euglena.
Make collections in bottles, carefully noting the habitat, and bring to Ges
laboratory for study.
72. Unicellular blue-green alge. Material of Glæocapsa or Oheoteos ;
Clathrocystis or Coelospherium is excellent. Study and draw :
1. The form and arrangement of the cells and cell colonies.
OSCILLATORIA 85
2. The structure of cellular envelopes if present.
3. The detailed structure of a cell; the color and its distribution. Are
chromatophores present ? Can you find a nucleus ? How do the cells
multiply ?
73. Oscillatoria.* *
A. Place a small mass of material in a watch glass full of
water. What is the color? After a few hours observe the
filaments radiating out from the central mass. Explain this
habit of growth after the study outlined in B.
B. Mount material well teased out. Under l.p. note:
1. The filaments. Are théy branched or unbranched? Are
they of uniform diameter ?
2. The movements of the filaments. Describe and diagram.
C. Under h.p. note and illustrate :
1. The cell structure at the tip of a filament and the par-
tition walls back of the tip. Compare the length and
breadth of the cells. What is their geometrical form ?
2. Draw a group of cells on a large scale, showing the dis-
tribution of their granular contents and the coloring
matter. (Are chromatophores present?! Can you find a
nucleus ? (Where are new partition walls formed ? )
3. Note the occasional dead cells. What is the form’ of the
cell wall on adjacent living cells and at the free tips of
filaments? Why should the wall take this form? The
presence of the dead cells weakens the filament, which
breaks apart readily at these points.
4. How do the cells multiply,/and how are new filaments
formed ? Is cell division confined to any particular region,
or is it general throughout the filament ?
5. Search for a very delicate sheath which holds the cells
together in a filament, like paper about a roll of coins.
D. Should material of Lyngbya be available, it may be studied
_advantageously at this point in comparison with Oscillatoria.
E. Dry a mass of Oscillatoria thoroughly, then pulverize and
place in a test tube with twice its bulk of water. After
86 TYPE STUDIES
several hours describe the color of the water as seen by
transmitted light and by reflected light. This color is due
to the pigment characteristic of the blue-green alge.
74. Nostoc or Anabaena.
A. Study the form and consistency of the colonies of Nostoc.
Make a habit sketch. Cut out a small portion from a colony
and crush under a cover glass. Note under Lp. :
1. The chains of cells, or filaments, imbedded in the almost
colorless jelly.
2 Are the filaments branched ? \continuous ?
B. Under h.p. draw part of a filament, showing :
1. The vegetative cells, their attachment to one another,
method of multiplication, and the character of the proto-
plasmic contents.
2. The occasional enlarged cells, heterocysts, empty or almost |
empty of cell contents. Two button-like plugs at the ends
of the heterocysts, which close what were formerly very.
small openings into the adjacent vegetative cells. How
are the heterocysts distributed throughout the filaments ?
From what are they developed ? Their function is not well
known, but the filaments tend to break apart at either side i
of these cells. How then are new filaments formed ?
C. Material of Anabæna with resting cells, or spores, is more 4
interesting than Nostoc, and furnishes an excellent compara- :
tive study with that type, or may be substituted for it. Study — _
the general morphology as in Nostoc, and especially the struc-
ture, position, and development of the resting cells.
REFERENCE (on the blue-green alge). Principles, Secs. 207—211.
Questions. What are some of the life conditions under which
the blue-green alge live? Describe the life history. How
may forms without differentiated resting cells, or spores (as
Oscillatoria), survive unfavorable seasons of drought or win-
ter? In what respects is the cell structure of these plants
simpler than that of Spirogyra? Compare the morphology
of the blue-green alge with that of the bacteria (if studied),
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PLEUROCOCCUS 87
75. Tolypothrix or Scytonema. These types are especially interesting for
the peculiar method of branching, called false branching. Study the general
morphology of the filament with special reference to the relation of the
branches to the heterocysts. Find the beginnings of a branch and note that
it breaks through the sheath which incloses the vegetative cells. The
heterocysts are more or less firmly united to the sheath, while the vegeta-
tive cells may slip along within it. The multiplication and growth of the
vegetative cells between the heterocysts, as fixed points, bring pressure to
bear which results in the rupture of the sheath and formation of a branch.
76. Glæotrichia. This type should be studied chiefly for the remarkable
resting cells, or spores, formed next the heterocysts at the bases of the radiat-
ing filaments, and for the attenuation of the filaments into long hairs,
THE GREEN ALGÆ, OR CHLOROPHYCEÆ
77. Field work on the green alge. The green alge live under a variety of
conditions, with several characteristic habitats: (1) there are the growths
in clear pools and ponds with floating filamentous masses (pond scums), free-
swimming forms (members of the Volvox family), attached filamentous or
expanded types (Gidogonium, Vaucheria, Chetophora, Coleocheete, etc.), and
the sediment, rich in desmids, diatoms, and many other one-celled types ;
(2) there are the growths in slowly running water of streams and on
the borders of lakes (frequently Ulothrix, Stigeoclonium, Draparnaldia,
Cladophora, and the stoneworts) ; (8) there are the growths just above and
below low-water mark on rocks along the seacoast (chiefly sea lettuces,
Ulothrix, and Cladophora) ; (4) there are the slimy growths on the trunks of
trees and stone walls (Pleurococcus and other one-celled relatives), and
filamentous forms on the earth (Vaucheria).
Studies should be made of some of these habitats, collections gathered
and examined in the laboratory, and the principal genera identified. Notes
should be taken in the field describing the appearance of the algæ as regards
size, texture, and color, and their growth habits in relation to light, depth
of immersion, and other factors,
78. Pleurococcus.* * Gather pieces of green stained bark from
the north side of trees, or scrapings from old fences.
A. Note the color and powdery appearance of the growth over
the surface and its thickness in places where the growth
separates as small scales. Moisten the bark and note the
brighter color.
a
—
a
88
TYPE STUDIES
. Scrape off some of the moistened Plewrococcus and mount in
water, well teased out. Examine under Lp. to find favorable
material. Under h.p. draw:
1. Groups of cells in outline, showing their loose attachment
to one another, except just after cell division, when the
daughter cells are to be found in pairs.
2. A single large cell, showing the cell wall and the proto-
plast; a nucleus can often be distinguished in the center
of the protoplast, and the chlorophyll is generally held in
a single large chromatophore which may or may not have a
pyrenoid. These points are brought out more clearly by
staining with iodine.
Questions. In what respects is the cell structure of Plewro-
coccus higher than that of the blue-green alge ? What is the
life history of Plewrococcus? Is it easily killed by winter’s
cold and summer’s drought, judging from its appearance on
trees and in other situations ? Make a study of the distri-
bution of Plewrococcus on a tree trunk, noting the limits of
growth and the regions of its greatest luxuriance. Try to
determine the reasons for the limits of growth.
79. Spherella or Volvox (App. 10). These types and others of the Volvos
family, when available, are especially interesting for their life habits and
cell structure, and in the higher types for the complex cell colonies and
methods of sexual reproduction.
A. In water swarming with Spherella note the reaction of the organism
to light when the vessel is placed near a window.
B. Under h.p. study the movements of the cell and the cell structure,
later killing and staining with iodine as described for Euglena
(Sec. 67, B). Note and draw :
1. The thick, somewhat gelatinous cell wall.
2. The protoplast with two cilia, red pigment spot, and large chromato-
phore. Which is the forward end as the organism swims ?
C. Should gametes be developed and begin to conjugate, or should the
large vegetative cells form thick-walled resting cells, these processes
may be studied,
D. Volvox as an example of a very highly organized cell colony may be
compared with Sphærella or other one-celled forms of the same family,
ERE = &"
ULOTHRIX 89
Study its swimming habits and its reaction to light in a vessel. Note the
points of similarity of its protoplasts to the cells of Spherella. Study
the structure of the cell colony and the method of forming daughter
colonies. Study the development of the eggs and their change into
odspores after fertilization, and, when material is present, the forma-
tion of the packets of sperms. Stained preparations may be studied
(Sec. 212).
REFERENCES (on the Volvox family). Goebel, 16, p. 34; Engler and Prantl,
39; Principles, Sec. 215.
80. Hydrodictyon, the water net (App. 11). This type, which is common
in some regions (as in parts of the East and Middle West), illustrates excep-
tionally well the features of a cell colony and its methods of reproduction.
The cells in older colonies are cenocytes, that is, contain many nuclei. They
have a large, irregular chromatophore with numerous pyrenoids. Permanent
preparations in balsam, stained with hematoxylin (Sec. 182), show these
points well. The pyrenoids are especially favorable for the study of starch
formation (see paper of Timberlake, Annals of Botany, Vol. XV, p. 619, 1901).
REFERENCE. Goebel, 16, p. 39; Principles, Fig. 179.
81. Ulothrix, Draparnaldia, or Stigeoclonium. Ulothrix is the best
for the study of zodspore formation, but the other types have a
more complex and interesting morphology.
A. Observe the attachment and appearance of the Beh
B. Pick off some filaments and mount in water. Under l.p.
study their general morphology./ Are they branched or un-
branched ? )Try to find the A cell of a filament with its
attachment, holdfast, and compare with the cells in the mid-
dle regions and at the ends. Make outline sketches illus-
trating these points. i growth confined to the tips, or is it
general throughontt the filament ? )
C. Under h.p. study the cell structure. Note:
1. The form of the cells, the band-like chromatophore with
pyrenoids. Draw in detail.
2. Stain with iodine to bring out the plasma membrane and
nucleus ; starch grains may be observed around the pyre-
noids.
D. Study the zodspores (best observed in the early morning
hours). In Ulothrix note: —
90
TYPE STUDIES
1. That the zodspores are developed in varying numbers in
the cells. Make counts and draw the various conditions.
Certain striking peculiarities of the zodspores, the pig-
ment spots (See 3), are easily recognized at this time.
2. The escape of the zodspores from the parent cells,
sporangia, and their swarming movement in the water.
They are sometimes called swarm spores.
8. The structure of the zodspore, showing pigment spot,
chromatophore, number and position of the cilia, gener-
ally four in number and made clear when material is
stained with iodine as described in Sec. 67, B. Which is
the forward end of the zodspore? Draw.
4. Should two-ciliate motile cells be present, they may be
expected to unite, or conjugate, in pairs in the water,
showing that they are sexual cells, or gametes. The prod-
ucts of the fusion are four-ciliate cells with two pigment
spots. These are zygospores, or zygotes.
Because the form or morphology of these gametes is similar,
this type of sexual reproduction is called isogamy.
E. Note that the zodspores gather on the illuminated side of
the vessel and settle down to germinate. After the material
has been in the vessel for three or four days, observe the
growth of young plants, or sporelings. Gather some of the
sporelings with a pipette and draw a number of stages illus-
trating the germination of the zodspore. Observe the older
sporelings, taking on the appearance of the parent plants, and
the development from the basal cell of a holdfast.
REFERENCE. Principles, Sec. 217.
Questions. Describe as fully as possible the life history of
Ulothrix or whatever other form may be studied. What
organisms do the zodspores resemble ? In what particulars ?
Of the two periods in the life history, the motile and quies-
cent, which represents the more primitive condition of
plant life? Which is now the more important for vegeta-
tive activities ? Which for reproductive ?
eee Aa
E.
ŒDOGONIUM 91
82. Ulva, the sea lettuce. Follow in general the outline for Ulothrix,
noting the different morphology of the plant but similar structure of the
individual cells. Study especially the margins of the thallus where zoöspores
may be developed.
REFERENCE. Principles, Sec. 218.
83. Cladophora. Follow an outline similar to that given for Ulothrix,
noting the different morphology and very different cell structure. The
older cells contain many nuclei, i.e. are cenocytes, and have either a net-
like chromatophore with pyrenoids, or numerous somewhat irregular chlo-
roplasts. Permanent preparations in balsam stained with hematoxylin
(Sec. 182) show these points well.
84. Zodspores, their formation and habits. Use good material of
Ulothrix, Draparnaldia, Stigeoclonium, Ulva, or Cladophora.
Place considerable fresh material in a glass vessel brightly
illuminated on one side. j
A. Zoöspores may be developed the next day, or perhaps a day
or so later. If formed, note:
1. At what time they appear in greatest quantity as a green
cloud, and in which part of the vessel.
2. Are they developed in the plant during the daytime ?
This will require the examination of material at various
times of day.
3. Can the time of their escape from the plant be delayed
by keeping material in the dark ?
B. A full study of the process of zoöspore formation would
require the killing and preservation of material at intervals
during the night.
85. Œdogonium.* *
A. Observe the habit of the plant, the general morphology of
the filaments. Are they branched or unbranched? Under
h.p. draw :
1. The end of a filament and some cells in the middle region
crossed at one end by delicate lines, the caps. Note the
large chromatophore almost filling the cell.
2. The remarkable disk-like holdfast developed by the basal
cell, especially well shown in younger plants.
92 TYPE STUDIES
B. Study fruiting material under h.p. Draw:
1. The female organ, or odgonium, which is a large swollen
cell that develops a single female gamete, the odsphere,
or egg. Note the rounding off of the egg before fertiliza-
tion as a naked protoplast, and the formation of a pore or
cleft to allow the entrance of the sperm.
2.,The odspore within the odgonium developed from the
fertilized egg, which forms a heavy wall about itself.
Observe the changed appearance of the cell contents, due
to the presence of much food material. Test for starch.
3. The male organs, or antheridia, groups of small disk-
shaped, almost colorless cells, each of which develops two
sperms. The sperms have a circle of cilia at one end.
Because the form or morphology of these gametes (eggs and
sperms) is unlike, this type of sexual reproduction is called
. heterogamy (meaning unlike gametes).
C. The large zodspores may be present in living material.
These are formed singly in the cells. Note their slow swim-
ming and the circle of cilia at one end.
Should the material of @dogoniwm be of a species with the
peculiar dwarf male plants, the laboratory directions would have
to be considerably changed.
REFERENCE (on the formation of the caps). Goebel, 16, p. 44.
Questions. What advances does @dogonium show over Ulo-
thria (1) in the structure of the vegetative cells, holdfasts,
and tip of filaments ? (2) in the sexual organs and gametes ?
Would the odspore from its structure be expected to ger-
minate at once, or is it fitted to carry the plant over unfavor-
able seasons? Describe the life history of @dogonium.
86. Coleochete (App. 12). If living material is available, study its expanded
growth over the substratum, as illustrated by some of the commonest species.
Preparations stained in hematoxylin (Sec. 212) and mounted entire in bal-
sam are excellent for detailed examination.
A. Under l.p. note the radiate arrangement of the cells from a center of
growth. Is the disk one layer of cells thick or more? Where does cell
a A
-
POND SCUMS 93
division and growth take place? May the disk be compared to a sys-
tem of radiating and branching filaments adhering to one another side
by side in a plane? Draw the outlines of several plants of different
ages, showing variety of form and appearance of lobes. Draw in detail
the cell structure of a sector from the center to the margin,
B. Search for sexual organs, odgonia and antheridia, near the margins of
the plants :
1. The odgonia become large cells, in most forms with a delicate exten-
sion like a long-necked flask, and each develops a single egg. The tip
of the extension opens, allowing the sperms to enter the odgonium.
2. The antheridia are small, almost colorless cells, generally present in
small groups near the margin. The sperms are two-ciliate.
3. After fertilization the egg forms a heavy wall about itself, thus
becoming an odspore. Short filaments then develop from the cell
under the odgonium, and these surround the oégonium with a cellular
protective envelope, and the entire structure becomes a conspicuous
fructification. i
87. Desmids. Excellent studies are furnished by species of Closterium,
Cosmarium, Docidium, Micrasterias, etc., and among.the filamentous forms
by Hyalotheca, Desmidium, etc. Make a general examination of sediment
from sunlit pools, or material skimmed or strained from the water, for a
favorable type.
A. Study the cell structure under h.p. Note and illustrate :
1.
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