A laboratory guide for a course in general botany,

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A LABORATORY GUIDE FOR A COURSE IN GENERAL BOTANY

A Textbook of General Botany.

Preface

Tus Guide had its origin in mimeographed directions for laboratory work, prepared five years ago and_ considerably revised and reprinted each year. ‘Two of the authors have worked together for these five years, and the third for three years, over the problems of organizing and teaching large classes in General Botany. On the basis of their experience at the University of California and elsewhere, they feel convinced that in many courses in elementary botany the number of structures, types, and topics presented is much too great for the student to assimilate properly. Very much more important than covering a great many subjects is a thorough study and fairly complete understanding of a few. . Furthermore, when a great variety of subjects are taken up in the laboratory, the student is likely to be hurried through a long series of set tasks without having an opportunity to realize what the object of most of them is. On that account, the authors have not attempted to introduce any laboratory work in Ecology, Genetics, or several other phases which might well be introduced if time were available to take up these subjects after a thorough and rather intensive study of the fundamentals of morphology and physiology.

These laboratory directions are designed for a year’s course of two periods weekly (each of two and one-half or three hours), but there should be no difficulty in so choosing exercises that the Guide may be used for a briefer course. There is no reason why the different divisions of the work should not be taken up in some other order than that in which they are presented here. When a change in the order results in the student’s encountering unfamiliar terms which have been defined or explained in earlier pages of the book, the glossary will furnish the needed definitions.

It is quite generally recognized by teachers that, in the case - of large elementary college classes of a hundred or more students, the study of the physiology of plants by means of experiments

Vi vl PREFACE carried on by the students themselves, is practically out of the question, unless large expenditures for duplicate equipment are made, specially equipped laboratories provided, and, what is most difficult of all, a considerable number of assistants, specially trained for such work, are available. On this account, the physiological exercises have been written in the form of directions for the observation of demonstrations; but these may be readily adapted by the teacher so that they will serve as directions for experiments by the students, if conditions favor the work being given in this way.

In the course at the University of California, several of the physiological exercises and one or two of the types in Part II have been omitted during the past few years.

In the Appendix, near the end of the book, the teacher will find a number of notes on collection, culture, and use of material, and on the conduct of the laboratory work. To avoid confusing the student, no references to these notes have been made in the text. These items have been arranged under the same headings as the laboratory directions, and it is suggested that the teacher refer to the notes on each group of exercises before those exercises are taken up in the laboratory.

The authors believe that, whenever possible, living material should be used for study, and that the student should cut his own sections and make his own preparations. Very satisfactory sections can be made by the student with a safety razor blade, after a little practice. Sectioning with a razor blade is easier for some when a razor blade holder is used. Several convenient forms of razor blade holders are now on the market.

In some cases it is impossible to avoid the use of stained and permanently mounted preparations. When these are used, it is desirable that living material of the plant in question be available in the laboratory for examination by the student and that the student make and examine rough preparations of this material before studying the slides. The prepared slides sold by the Biological Supply Companies are often unsatisfactory, but one of the best of these companies has made, according to our instructions, a set of all the slides called for in this manual. The company’s address is given in the Appendix on page 85.

The authors believe, as mentioned above, that training in careful and precise observation, thinking and expression, and a

PREFACE | Vii clear understanding of the fundamentals of plant structure, development, and functions are the most important ends to be sought in a course of this sort. On that account they favor a rather intensive study of a few plants instead of a more superficial survey of many forms. At the same time, they realize that it is possible for a student to study quite intensively a single fern or conifer, or flowering plant, and yet know very little about ferns as a group or about conifers or flowering plants as a group. They have therefore introduced into the course some exercises on the determination, by means of keys, of some of the commoner ferns, conifers, and angiosperms.

SEPTEMBER, 1925. LEE BoNAR.

RicHarRp M. HoLMaAn.

Lucite Rovusu.

TO THE STUDENT

In the laboratory the student will be expected to examine closely the material furnished for study in order to make out all the details of structure that can be seen by the naked eye, or in other cases by the use of the dissecting microscope or the compound microscope. The habit of close scrutiny of natural objects is essential for any person who is entering upon scientific study. Such careful examination, even without the microscope, will often reveal, even in the case of plant parts with which the student - may believe himself thoroughly familiar, structures, the existence of which he has never suspected.

As an aid in this searching examination of the material and as a proof that the parts present have been seen, the student will be required to draw many plant structures studied in the laboratory. The drawing is not an end in itself. Mere talent in drawing will in no case be made the basis for credit, but each student will be expected to do this work to the best of his ability. Not infrequently, students with natural ability in drawing do less satisfactory work, on account of failure to make out important details, than others who are without natural ability or training in drawing and who may even doubt, at the beginning, their ability to represent the objects studied. Satisfactory drawings can be made by practically any student who makes a reasonable effort.

SCIENTIFIC NAMES OF PLANTS

Although common names of plants are useful and largely employed in applied botany, they can not take the place of scientific names, for a single plant may have many different common names in one locality and the common name of a plant often varies in different localities. Furthermore, several species, often not closely related, may have the same common name. For these reasons the scientific name is employed not only in pure botany, x TO THE STUDENT but in applied botany (forestry, horticulture, agronomy, etc.), when any but the most generally known species are referred to. The scientific name consists of two parts, the generic name, or genus name, and the specific, or species name. The generic name always begins with a capital. Several kinds of plants (species) may belong to a single genus. Thus Pinus is the genus of the pines, of which there are many species, as Pinus ponderosa (yellow pine), Pinus radiata (Monterey pine), etc. So also Triticum is the genus of wheat, but included in this genus are Triticum polonicum (Polish wheat), Triticum dicoccum (emmer), Triticum vulgare (common wheat), Triticum durum (durum wheat), and others. Just as a number of closely related species make a genus, so several closely related genera make a family, several families an order, several orders a class, and several classes a division.

Contents

Books FOR REFERENCE AND COLLATERAL READING..............+.. XV

TYPES OF THE PRINCIPAL GROUPS OF PLANTS

Schizomycetes or Bacteria... a vee eee eee PhycomycetessorsAlgal Wungi.22.4:.e toe eee Ascomycetesior Ascus' Funel,;.. 2... 10 eee ee Basidiomycetes or Basidium: Fungi.2.-.... 2s ee eee

Part I THE PLANT CELL

Aut plants are made up of structural units called cells, and all the activities of plants are directly dependent on the activities of some of these structural units. On that account we shall first study the structure and some of the activities of plant cells. This will be followed by an examination of the principal kinds of tissues (groups of similar cells adapted to a given function) found in plants, so that in the subsequent study of the different organs of the plant, the tissues of which they are constructed may be recognized. After the relation of the various organs of the plant have been briefly studied under the heading, ‘‘ The Plant as a Whole,” the different organs of the seed-bearing plant will be taken up in succession.

READING ASSIGNMENT:

Holman and Robbins, pp. 13-39.

Stevens, Plant Anatomy, Chapter I.

1. Stem tips of pumpkin (Cucurbita pepo), squash (Cucurbita maxima), or almost any other member of the squash family (Cucurbitaceae).

2. Scales from the bulb of onion (Allium).

3. Shoots of Hlodea, an aquatic seed plant.

4. Fruits of red bell pepper (Capsicum annuum), tomato (Lycopersicum esculentum), and carrot (Daucus carota); the petals of some yellow flowers or of pansy (Vvola tricolor).

2 THE PLANT CELL

5. Leaves of the striped-leaf wandering Jew (Zebrina pendula), or leaves of Iresine Lindeni or other species of that genus. 6. Stained and permanently mounted longitudinal sections of the root tip of onion (Alliwm), showing nuclei in division.

1. With your razor blade, cut from near the extreme tip of a squash or pumpkin stem several rather thin cross sections. Mount in water on a slide and cover with a cover glass. Examine these sections with the low power of the compound microscope and study the form and structure of the two types of hairs (pointed and capitate).

Draw a large, uninjured, and typical pointed hair as seen with the low power, but on a large scale (not shorter than 4 inches).

All the details visible with the low power should be accurately shown. Note that changes in the illumination, affected by moving the mirror or adjusting the iris diaphragm, often bring out details of structure more clearly.

Find a large cell that shows clearly all the cell structures and the streaming of the cytoplasm. Draw this cell on a large scale as seen with h. p.* Indicate the movement of the cytoplasm by arrows. The cytoplasm can be best represented by stippling (numerous small, equally spaced dots).

2. Strip a piece of the epidermis from the inner surface of an onion scale and mount in water. Examine the cells with the low and with the high power. Note whether any of the structures seen in the squash or pumpkin hair are lacking from these cells, and study the streaming of the cytoplasm, which can best be seen near the ends of the cells. Draw a single cell on a large scale.

3. Remove several of the younger leaves from a shoot of Elodea. Mount, and examine with |. p. and h. p. Look for the structures seen in the cells of the hairs of the squash or pumpkin. What structures are you unable to locate? Note the difference between the views secured when the microscope is focused on the upper or lower surface of the cell (surface view) and when it is focused halfway between the two surfaces (median optical section). Draw two diagrams showing a cell as seen in these two views. In these diagrams the number and forms of the green bodies

* From this point on, the low power of the compound microscope will be indicated by the letters “1. p.”’, the high power by “‘h. p.”

(chloroplasts) should be accurately shown. In at least one of these diagrams, indicate the course of the streaming cytoplasm by means of small arrows. Find chloroplasts which appear to be dividing. Draw such a chloroplast on a large scale.

4. Cut a thin section through the flesh of the tomato or pepper fruit at right angles to the surface, mount, and study with 1. p. and h. p. Draw on a large scale at least two cells showing all the structures in the cells and particularly the orange-colored chromoplasts. The latter structures soon undergo change of form when placed in water. On that account, the drawings should be made from material recently mounted. Draw also several chromoplasts on a much larger scale.

5. Clean two slides. On one place a large drop of water and on the other a drop of the 20 per cent cane sugar solution which will be found in a dropping bottle on the laboratory table. Strip pieces of the colored epidermis from the lower side of a leaf of Zebrina or Iresine. Mount several pieces, surface side up, on each of the slides. Cover with cover glasses and examine at three-minute intervals until a marked change, most clearly visible in the colored cells, has taken place in some of the colored cells of one of the preparations. Then draw two or three of the altered cells and a like number from the other preparation. Explain the reasons for the change observed (plasmolysis). Remove the cover glass from the preparation mounted in sugar, wipe off most of the solution and replace it with water. Then cover with a cover glass and examine from time to time under the microscope to see if the altered cells regain their original condition.

6. With |. p. examine the stained sections of onion root tip which are furnished you. Note the form of the cells in different parts of the sections and the length of the cells as compared with the width. Observe also whether the cells near the pointed end or those farther back have the denser cell contents. Among the small cells near the pointed end, find and study with h. p. one that shows clearly the cytoplasm; and the nucleus with its membrane, nucleoli (singular nucleolus), chromatin granules, and fine net-work of linin. Nuclei showing all these structures are said to be in the resting condition. Make a large-scale drawing of a cell with resting nucleus.

Some of the cells in the region of the extreme tip will be found to have nuclei which are undergoing nuclear division, or mitosis.

4 THE PLANT CELL

The instructor will explain this process if it has not already been discussed in the lectures. Draw diagrams of at least four different stages in the process of mitosis as seen under the demonstration microscopes set up by the instructor.

1. DistincTION BETWEEN PURE SUBSTANCES, TRUE SOLUTIONS, COLLOIDAL SOLUTIONS AND HETEROGENEOUS MIXTURES a. Pure substances are of two kinds, elements and compounds. Familiar examples of elements are sulphur, mercury (quicksilver) and aluminum. More than eighty such elements are known; from these, all other substances are made up. An element can not be changed into any other substance except by adding another element or elements to it and thus forming a compound.

A compound always consists of two or more elements united in certain definite and constant proportions. Familiar examples of compounds are water, common salt, and carbon dioxide. Water is a compound of the two elements, hydrogen and oxygen, in the proportion, by volume, of 2 to 1. Common salt is a compound of the elements, sodium and chlorine, in the proportions, by weight, of about 23 to 35.5. The smallest quantity, or unit, of a compound, is called a molecule, and the particles of elements which unite to form molecules of a compound are called atoms. Several atoms of a element can also combine to form a molecule of an element. Thus, oxygen gas is made up of oxygen molecules, each consisting of two oxygen atoms. Briefly, then, a pure substance is a substance the molecules of which are of one kind only. If more than one kind of atom is present in a pure substance, the substance is a compound; if only one kind, the substance is an element.

b. A quantity of matter in which more than one kind of molecule is present is spoken of as a mixture; that is to say, any material consisting of two or more pure substances not united into a compound is a mixture. The elements in a compound are always present in certain definite and constant proportions, but a mixture may vary greatly as to the proportions of its constituents. Mixtures are of two principal kinds: true solutions and heterogeneous mixtures. If a small quantity of the pure substance, salt, is added to the pure substance, water, and the container is shaken or its contents stirred, the salt disappears. As the salt goes into solution in the water, the salt molecules become separated from one another and uniformly distributed through the water. The largest particles in such a true solution are molecules; and, since molecules are too small to be seen by even the highest powers of the microscope, the different constituents of a true solution can not be distinguished by the eye.

A true solution differs from a compound in two respects: first, in that it consists of at least two kinds of molecules; and second, in that the proportions of the components may vary. Thus, salt solutions may contain any concentration of salt from only a trace to thirty parts or more of salt to one hundred of water. Solutions are generally liquid, but there are also gaseous solutions (air) and solid solutions.

If the particles of one or more of the substances in a mixture are larger than molecules, the mixture is a heterogeneous mixture. A piece of granite is a heterogeneous mixture consisting of particles of different kinds of rock, clearly visible to the eye. Similarly, a mixture of white sand and sugar is a heterogeneous mixture. The particles can be readily distinguished by the use of a lens or a microscope, and are many times larger than molecules.

A particular kind of heterogeneous mixture which is of great interest, especially to botanists and zoologists, is the colloidal solution. In most colloidal solutions one or more of the components is mixed with a liquid, and is in so fine a state of division (either as tiny solid particles or as droplets) that it does not tend to settle out, or at least settles out very slowly. The suspended particles of a colloidal solution may be too small to be seen by the most powerful microscopes, but are larger than molecules. In such cases a colloidal solution may appear perfectly clear, like a true solution. If an intense beam of light is passed through a colloidal solution, however, the path of the beam will be distinctly visible where it passes through the solution because the colloidal particles in suspension are large enough to reflect the light. If a true solution (for example, salt in distilled water) is used, the path of the light through the solution will not be visible, because the particles in suspension are not large enough to reflect the light.

c. Something of the significance of the subjects just discussed,

Bain THE PLANT CELL in connection with the plant cell, will be made clear by the following statements in which the terms defined above are used:

The protoplast of a plant cell is generally surrounded by a wall composed of the compound, cellulose, the molecules of which are made up of atoms of the elements carbon, hydrogen and oxygen. Everything that enters the plant cell, must be in the form of a true solution for substances in colloidal solution can not pass through the wall or the cytoplasmic membrane of the protoplast. The cytoplasm itself is a colloidal solution in which very small particles of proteins and other substances are suspended in a watery true solution. The liquid filling the vacuoles is a true solution of many substances, including certain gases, dissolved in water. The cytoplasmic membrane prevents or greatly restricts the movement of certain molecules into or out of the cell, even though they are in true solution.

2. DIFFUSION

There will be set up in the laboratory a water-filled glass cylinder or tube at the bottom of which has been placed a piece of copper sulphate or other soluble colored substance. The vessel should not be touched or jarred. Observe from day to day, and note how long a time passes before the liquid becomes equally colored throughout. What does a difference in intensity of the color indicate as to the distribution of the particles of the dissolved substance? What keeps the dissolved particles of a substance, which is heavier than water, in suspension after it has dissolved?

3. OSMOSIS AND Osmotic PRESSURE

Observe the apparatus (osmoscope) set up in the laboratory to demonstrate that when. a solution is separated from water or from a less concentrated solution of the same components by a membrane through which the dissolved substance can not pass, or passes very slowly, a pressure arises. Explain why the volume of the solution within the osmoscope increases, and state what evidence there is of pressure within the osmoscope. Make a diagram of the apparatus and explain fully. Compare the apparatus to a living cell immersed in water.

4. RELATIVE DIFFUSIBILITY OF SUBSTANCES IN TRUE AND COLLOIDAL SOLUTION

A dialyzer (a sac of parchment paper or collodion), containing a diluted starch paste to which some common salt has been added, is placed in a beaker of distilled water. Care should be taken that none of the contents of the dialyzer is spilled into the water. After several hours, one portion of the water will be tested for starch by adding some iodine solution, which gives-a blue color in the presence of starch; and another portion for common salt, by adding a little silver nitrate solution, which will give a white precipitate if salt is present. Which, if either, of the two substances (starch or salt) diffused through the membrane? What circumstance determines which substance, if either, is retained and which passes through?

5. Errect oF TurRGoR ON LENGTH AND RiIGIpITY OF TISSUE

By means of a cork borer cylinders about 8-10 millimeters in diameter and 6-10 centimeters in length are cut from potato tubers, and trimmed to exactly the same length. Some of them are placed in pure water, others in a very concentrated salt solution, and still others are boiled for five minutes. Compare the length and rigidity of the cylinders after half an hour, and account for the differences, if any are observed. ‘This demonstration (or experi- ~ ment) can also be performed with rhubarb or the fleshy peduncle of such flowers are -Richardia (calla) or Amaryllis. If either of these plants is available the demonstrations (or experiment) should be repeated with it. Endeavor to explain any difference between the results obtained and those observed in the case of the potato tissue.

6. DEMONSTRATION OF EFFECT OF DEATH ON THE PERMEABILITY OF THE CYTOPLASMIC MEMBRANE

Examine the microscopic demonstration of sections of red beet. Determine whether the red color is present in chromoplasts or is dissolved in the cell sap. Compare two test tubes containing thin slices of red beet which, after being washed, have been placed in pure water. The slices in one tube have been boiled. Explain any difference in the appearance of the two preparations.

8 THE PLANT CELL

7. RESPIRATION

There is constantly taking place in the living cells of all plants and animals a process called respiration, by which complex substances in the cell, such as grape sugar (CgHi20¢), are broken down into simple compounds such as carbon dioxide (COz) and water (H20).

In most cases the plant or animal is unable to carry on this process unless it can absorb oxygen, for oxygen is necessary to ordinary respiration just as it is to the somewhat similar process of combustion, or burning. Respiration involves the destruction of useful substances. It is, nevertheless, essential to the life of the cell, and therefore of the whole plant or animal, for it furnishes energy which is necessary for various processes that must go on in the cells.

Observe, and report fully in writing, the following demonstrations:

I. To show that baryta water (solution of bariwm hydroxide) or lime water (solution of calcium hydroxide) when in contact with carbon dioxide gas forms a white precipitate: A stream of carbon dioxide from a cylinder of the gas is permitted to bubble through a quantity of clear baryta water or lime water.

II. To show that the atmosphere contains carbon dioxide: A quantity of lime water or baryta water is exposed to the air in a shallow vessel.

III. To show that air may be deprived of carbon dioxide by being passed through a solution of caustic potash (potassium hydroxide): Air is caused (a) to bubble through water and then through barium hydroxide solution (baryta water), and (b) to bubble through a solution of caustic potash and then through barium hydroxide solution.

IV. To show that carbon dioxide (a product of respiration) is present in considerable quantity in the air exhaled from the lungs: The demonstrator blows his breath into clear lime water or baryta water through a tube.

V. To show that carbon dioxide is gwen out by. plant tissue: The apparatus consists of a series of five bottles or flasks, so connected by rubber stoppers and tubing that a stream of air can be drawn through the whole series without any of the liquid contained in the first, second, fourth, or fifth containers leaving these vessels.

The five vessels contain respectively: (1) caustic potash solution, (2) baryta water, (3) leaves, germinating seeds or other living plant tissue, (4) baryta water, and. (5) caustic potash solution. Air is drawn through this series of vessels by means of a filter pump or aspirator. In describing this demonstration the student should not fail to explain why each of the four solutions is used, and should also make a neat diagram of the apparatus.

VI. To show that when respiration is prevented by depriving the plant of oxygen, normal growth and development are interfered with: Two lots of soaked seeds are placed in enclosed chambers, the plant of oxygen, normal growth and development are interfered with: Two lots of soaked seeds are placed in enclosed chambers, A and B, from one of which (B) all oxygen has been removed by means of an oxygen-absorbing solution (potassium pyrogallate). The seeds are left in these chambers in the dark (Why?) for several days and then observed. A neat diagram of the apparatus should accompany the account of this demonstration.

Before passing on to the next exercise, the student should answer the following questions:

What is a cell? Name the parts of a typical green plant cell. How does a typical plant cell differ from a typical animal cell? What is a protoplast? Protoplasm? Cytoplasm? Name the parts of the nucleus. What do the vacuoles of plant cells contain? Of what material is the cell wall composed? Which of the following are dead, which living: nucleus, cell wall, vacuoles, cell sap, cytoplasm, plastids? What is a chromoplast? Of what use to a plant may the pigments in its cells be? Explain, as fully as you can, what happens when a living cell is placed in a concentrated solution of sugar. Does the process necessarily kill the cell? What happens if the cell is placed in water again after a little while? What structures in the cell bear the hereditary characters? In what condition of the cell are these structures most easily seen?

What is meant by a semi-permeable membrane? Explain wilting. State a number of ways in which it may be caused. Can a wilted plant recover its normal condition? How? Explain what is meant by turgor. How is the number of cells of a plant increased? Give an account of the changes which the nucleus

10 PLANT TISSUES undergoes during cell division. Contrast the processes of photosynthesis and respiration. Which process, if either, is restricted to animals? Why? Which, if either, to plants? Why? Is either process restricted to certain kinds of plant cells? If so, to what cells and why?

PLANT TISSUES

In the simplest of plants, such as the Bacteria and certain of the Algae, the whole plant body consists of a single cell which is capable of performing, and does in fact perform, all the vital functions. In other simple plants the plant body consists of a small group of cells which are practically all alike. In many such plants every cell carries on all of the processes necessary to life. In most plants, however, there are thousands of cells and these are of different kinds according to the functions which the different groups perform for the whole plant. The cells differ in many ways, i.e., length, width, thickness of cell wall, presence or absence of spaces between them (intercellular spaces), presence of thin places (pits) in the cell walls, chemical nature of the cell walls, ete. A group of similar cells having a common origin and a common function is called a tissue.

READING ASSIGNMENT:

Holman and Robbins, pp. 42-48.

Stevens, Chapters IV and V.

1. Leaves of dock (Rumex). Stem of tomato (Lycopersicum).

2. Shoots of wandering Jew (Tradescantia sp.).

3. Leaves of New Zealand flax (Phormium tenax). Linum or other plant having abundant and typical bast fibers.

4, Stained cross and longitudinal sections of Dutchman’s pipe (Aristolochia), Platanus, apple, or other woody stem.

5. Stained cross, tangential and radial sections of the wood of pine (Pinus).

1. With a razor blade, make thin sections of the petiole (leaf stalk) of Rumex, or of the stem of tomato. Mount in water