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STRUCTURAL AND SYSTEMATIC BOTANY,
FOR HIGH SCHOOLS AND ELEMENTARY COLLEGE COURSES.
BY DOUGLAS HOUGHTON CAMPBELL, PH.D., PROFESSOR OF BOTANY IN THE INDIANA UNIVERSITY.
BOSTON, U.S.A.: PUBLISHED BY GINN & COMPANY. 1890.
COPYRIGHT, 1890, BY DOUGLAS HOUGHTON CAMPBELL.
ALL RIGHTS RESERVED.
TYPOGRAPHY BY J. S. CUSHING & CO., BOSTON, U.S.A. PRESSWORK BY GINN & CO., BOSTON, U.S.A.
The rapid advances made in the science of botany within the last few years necessitate changes in the text books in use as well as in methods of teaching. Having, in his own experience as a teacher, felt the need of a book different from any now in use, the author has prepared the present volume with a hope that it may serve the purpose for which it is intended; viz., an introduction to the study of botany for use in high schools especially, but sufficiently comprehensive to serve also as a beginning book in most colleges.
It does not pretend to be a complete treatise of the whole science, and this, it is hoped, will be sufficient apology for the absence from its pages of many important subjects, especially physiological topics. It was found impracticable to compress within the limits of a book of moderate size anything like a thorough discussion of even the most important topics of all the departments of botany. As a thorough understanding of the structure of any organism forms the basis of all further intelligent study of the same, it has seemed to the author proper to emphasize this feature in the present work, which is professedly an introduction, only, to the science.
This structural work has been supplemented by so much classification as will serve to make clear the relationships of different groups, and the principles upon which the classification is based, as well as enable the student to recognize the commoner types of the different groups as they are met with. The aim of this book is not, however, merely the identification of plants. We wish here to enter a strong protest against the only too prevalent idea that the chief aim of botany is the ability to run down a plant by means of an "Analytical Key," the subject being exhausted as soon as the name of the plant is discovered. A knowledge of the plant itself is far more important than its name, however desirable it may be to know the latter.
In selecting the plants employed as examples of the different groups, such were chosen, as far as possible, as are everywhere common. Of course this was not always possible, as some important forms, e.g. the red and brown seaweeds, are necessarily not always readily procurable by all students, but it will be found that the great majority of the forms used, or closely related ones, are within the reach of nearly all students; and such directions are given for collecting and preserving them as will make it possible even for those in the larger cities to supply themselves with the necessary materials. Such directions, too, for the manipulation and examination of specimens are given as will make the book, it is hoped, a laboratory guide as well as a manual of classification. Indeed, it is primarily intended that the book should so serve as a help in the study of the actual specimens.
Although much can be done in the study, even of the lowest plants, without microscopic aid other than a hand lens, for a thorough understanding of the structure of any plant a good compound microscope is indispensable, and wherever it is possible the student should be provided with such an instrument, to use this book to the best advantage. As, however, many are not able to have the use of a microscope, the gross anatomy of all the forms described has been carefully treated for the especial benefit of such students. Such portions of the text, as well as the general discussions, are printed in ordinary type, while the minute anatomy, and all points requiring microscopic aid, are discussed in separate paragraphs printed in smaller type.
The drawings, with very few exceptions, which are duly credited, were drawn from nature by the author, and nearly all expressly for this work.
A list of the most useful books of reference is appended, all of which have been more or less consulted in the preparation of the following pages.
The classification adopted is, with slight changes, that given in Goebel's "Outlines of Morphology and Classification"; while, perhaps, not in all respects entirely satisfactory, it seems to represent more nearly than any other our present knowledge of the subject. Certain groups, like the Diatoms and Characeae, are puzzles to the botanist, and at present it is impossible to give them more than a provisional place in the system.
If this volume serves to give the student some comprehension of the real aims of botanical science, and its claims to be something more than the "Analysis" of flowers, it will have fulfilled its mission.
DOUGLAS H. CAMPBELL.
BLOOMINGTON, INDIANA, October, 1889.
TABLE OF CONTENTS.
PAGE CHAPTER I.—INTRODUCTION 1
Composition of Matter; Biology; Botany; Zooelogy; Departments of Botany; Implements and Reagents; Collecting Specimens.
CHAPTER II.—THE CELL 6
Parts of the Cell; Formation of New Cells; Tissues.
CHAPTER III.—CLASSIFICATION OF PLANTS 9
Protophytes; Slime-moulds; Schizophytes; Blue-green Slimes, Oscillaria; Schizomycetes, Bacteria; Green Monads, Euglena, Volvox.
CHAPTER IV.—ALGAE 21
Classification of Algae; Green Algae; Protococcaceae, Protococcus; Confervaceae, Cladophora, OEdogonium, Coleochaete.
CHAPTER V.—GREEN ALGAE (Continued) 30
Pond-scums, Spirogyra; Siphoneae, Vaucheria; Characeae, Chara.
CHAPTER VI.—BROWN SEAWEEDS 41
Diatomaceae; True Brown Algae, Fucus; Classification of Brown Algae.
CHAPTER VII.—RED ALGAE 49
Structure of Red Algae; Callithamnion; Fresh-Water Forms.
CHAPTER VIII.—FUNGI 54
Phycomycetes, Mycomycetes; Phycomycetes, Black Moulds, Mucor; White Rusts and Mildews, Cystopus; Water Moulds.
CHAPTER IX.—TRUE FUNGI 63
Yeast; Smuts; Ascomycetes; Dandelion Mildew; Cup Fungi, Ascobolus; Lichens; Black Fungi.
CHAPTER X.—TRUE FUNGI (Continued) 77
Basidiomycetes; Rusts; Coprinus; Classification.
CHAPTER XI.—BRYOPHYTES 86
Classification; Liverworts, Madotheca; Classification of Liverworts; Mosses, Funaria; Classification of Mosses.
CHAPTER XII.—PTERIDOPHYTES 102
Bryophytes and Pteridophytes; Germination and Prothallium; Structure of Maiden-hair Fern.
CHAPTER XIII.—CLASSIFICATION OF PTERIDOPHYTES 116
Ferns; Horse-tails; Club Mosses.
CHAPTER XIV.—SPERMAPHYTES 128
General Characteristics; Gymnosperms and Angiosperms, Scotch-pine; Classification of Gymnosperms.
CHAPTER XV.—SPERMAPHYTES (Continued) 143
Angiosperms; Flowers of Angiosperms; Classification of Angiosperms; Monocotyledons, Structure of Erythronium.
CHAPTER XVI.—CLASSIFICATION OF MONOCOTYLEDONS 153
Liliiflorae; Enantioblastae; Spadiciflorae; Glumaceae; Scitamineae; Gynandrae, Helobiae.
CHAPTER XVII.—DICOTYLEDONS 170
General Characteristics; Structure of Shepherd's-purse.
CHAPTER XVIII.—CLASSIFICATION OF DICOTYLEDONS 181
Choripetalae: Iuliflorae; Centrospermae; Aphanocyclae; Eucyclae; Tricoccae; Calyciflorae.
CHAPTER XIX.—CLASSIFICATION OF DICOTYLEDONS (Continued) 210
Sympetalae: Isocarpae, Bicornes, Primulinae, Diospyrinae; Anisocarpae, Tubiflorae, Labiatiflorae, Contortae, Campanulinae, Aggregatae.
CHAPTER XX.—FERTILIZATION OF FLOWERS 225
CHAPTER XXI.—HISTOLOGICAL METHODS 230
Nuclear Division in Wild Onion; Methods of Fixing, Staining, and Mounting Permanent Preparations; Reference Books.
All matter is composed of certain constituents (about seventy are at present known), which, so far as the chemist is concerned, are indivisible, and are known as elements.
Of the innumerable combinations of these elements, two general classes may be recognized, organic and inorganic bodies. While it is impossible, owing to the dependence of all organized matter upon inorganic matter, to give an absolute definition, we at once recognize the peculiarities of organic or living bodies as distinguished from inorganic or non-living ones. All living bodies feed, grow, and reproduce, these acts being the result of the action of forces resident within the organism. Inorganic bodies, on the other hand, remain, as a rule, unchanged so long as they are not acted upon by external forces.
All living organisms are dependent for existence upon inorganic matter, and sooner or later return these elements to the sources whence they came. Thus, a plant extracts from the earth and air certain inorganic compounds which are converted by the activity of the plant into a part of its own substance, becoming thus incorporated into a living organism. After the plant dies, however, it undergoes decomposition, and the elements are returned again to the earth and atmosphere from which they were taken.
Investigation has shown that living bodies contain comparatively few elements, but these are combined into extraordinarily complex compounds. The following elements appear to be essential to all living bodies: carbon, hydrogen, oxygen, nitrogen, sulphur, potassium. Besides these there are several others usually present, but not apparently essential to all organisms. These include phosphorus, iron, calcium, sodium, magnesium, chlorine, silicon.
As we examine more closely the structure and functions of organic bodies, an extraordinary uniformity is apparent in all of them. This is disguised in the more specialized forms, but in the simpler ones is very apparent. Owing to this any attempt to separate absolutely the animal and vegetable kingdoms proves futile.
The science that treats of living things, irrespective of the distinction between plant and animal, is called "Biology," but for many purposes it is desirable to recognize the distinctions, making two departments of Biology,—Botany, treating of plants; and Zooelogy, of animals. It is with the first of these only that we shall concern ourselves here.
When one takes up a plant his attention is naturally first drawn to its general appearance and structure, whether it is a complicated one like one of the flowering plants, or some humbler member of the vegetable kingdom,—a moss, seaweed, toadstool,—or even some still simpler plant like a mould, or the apparently structureless green scum that floats on a stagnant pond. In any case the impulse is to investigate the form and structure as far as the means at one's disposal will permit. Such a study of structure constitutes "Morphology," which includes two departments,—gross anatomy, or a general study of the parts; and minute anatomy, or "Histology," in which a microscopic examination is made of the structure of the different parts. A special department of Morphology called "Embryology" is often recognized. This embraces a study of the development of the organism from its earliest stage, and also the development of its different members.
From a study of the structure of organisms we get a clue to their relationships, and upon the basis of such relationships are enabled to classify them or unite them into groups so as to indicate the degree to which they are related. This constitutes the division of Botany usually known as Classification or "Systematic Botany."
Finally, we may study the functions or workings of an organism: how it feeds, breathes, moves, reproduces. This is "Physiology," and like classification must be preceded by a knowledge of the structures concerned.
For the study of the gross anatomy of plants the following articles will be found of great assistance: 1. a sharp knife, and for more delicate tissues, a razor; 2. a pair of small, fine-pointed scissors; 3. a pair of mounted needles (these can be made by forcing ordinary sewing needles into handles of pine or other soft wood); 4. a hand lens; 5. drawing-paper and pencil, and a note book.
For the study of the lower plants, as well as the histology of the higher ones, a compound microscope is indispensable. Instruments with lenses magnifying from about 20 to 500 diameters can be had at a cost varying from about $20 to $30, and are sufficient for any ordinary investigations.
Objects to be studied with the compound microscope are usually examined by transmitted light, and must be transparent enough to allow the light to pass through. The objects are placed upon small glass slips (slides), manufactured for the purpose, and covered with extremely thin plates of glass, also specially made. If the body to be examined is a large one, thin slices or sections must be made. This for most purposes may be done with an ordinary razor. Most plant tissues are best examined ordinarily in water, though of course specimens so mounted cannot be preserved for any length of time.
 For the mounting of permanent preparations, see Chapter XIX.
In addition to the implements used in studying the gross anatomy, the following will be found useful in histological work: 1. a small camel's-hair brush for picking up small sections and putting water in the slides; 2. small forceps for handling delicate objects; 3. blotting paper for removing superfluous water from the slides and drawing fluids under the cover glass; 4. pieces of elder or sunflower pith, for holding small objects while making sections.
In addition to these implements, a few reagents may be recommended for the simpler histological work. The most important of these are alcohol, glycerine, potash (a strong solution of potassium hydrate in water), iodine (either a little of the commercial tincture of iodine in water, or, better, a solution of iodine in iodide of potassium), acetic acid, and some staining fluid. (An aqueous or alcoholic solution of gentian violet or methyl violet is one of the best.)
A careful record should be kept by the student of all work done, both by means of written notes and drawings. For most purposes pencil drawings are most convenient, and these should be made with a moderately soft pencil on unruled paper. If it is desired to make the drawings with ink, a careful outline should first be made with a hard pencil and this inked over with India-ink or black drawing ink. Ink drawings are best made upon light bristol board with a hard, smooth-finished surface.
When obtainable, the student will do best to work with freshly gathered specimens; but as these are not always to be had when wanted, a few words about gathering and preserving material may be of service.
Most of the lower green plants (algae) may be kept for a long time in glass jars or other vessels, provided care is taken to remove all dead specimens at first and to renew the water from time to time. They usually thrive best in a north window where they get little or no direct sunshine, and it is well to avoid keeping them too warm.
Numbers of the most valuable fungi—i.e. the lower plants that are not green—grow spontaneously on many organic substances that are kept warm and moist. Fresh bread kept moist and covered with a glass will in a short time produce a varied crop of moulds, and fresh horse manure kept in the same way serves to support a still greater number of fungi.
Mosses, ferns, etc., can be raised with a little care, and of course very many flowering plants are readily grown in pots.
Most of the smaller parasitic fungi (rusts, mildews, etc.) may be kept dry for any length of time, and on moistening with a weak solution of caustic potash will serve nearly as well as freshly gathered specimens for most purposes.
When it is desired to preserve as perfectly as possible the more delicate plant structures for future study, strong alcohol is the best and most convenient preserving agent. Except for loss of color it preserves nearly all plant tissues perfectly.
If we make a thin slice across the stem of a rapidly growing plant,—e.g. geranium, begonia, celery,—mount it in water, and examine it microscopically, it will be found to be made up of numerous cavities or chambers separated by delicate partitions. Often these cavities are of sufficient size to be visible to the naked eye, and examined with a hand lens the section appears like a piece of fine lace, each mesh being one of the chambers visible when more strongly magnified. These chambers are known as "cells," and of them the whole plant is built up.
In order to study the structure of the cell more exactly we will select such as may be examined without cutting them. A good example is furnished by the common spiderwort (Fig. 1). Attached to the base of the stamens (Fig. 85, B) are delicate hairs composed of chains of cells, which may be examined alive by carefully removing a stamen and placing it in a drop of water under a cover glass. Each cell (Fig. 1) is an oblong sac, with a delicate colorless wall which chemical tests show to be composed of cellulose, a substance closely resembling starch. Within this sac, and forming a lining to it, is a thin layer of colorless matter containing many fine granules. Bands and threads of the same substance traverse the cavity of the cell, which is filled with a deep purple homogeneous fluid. This fluid, which in most cells is colorless, is called the cell sap, and is composed mainly of water. Imbedded in the granular lining of the sac is a roundish body (n), which itself has a definite membrane, and usually shows one or more roundish bodies within, besides an indistinctly granular appearance. This body is called the nucleus of the cell, and the small one within it, the nucleolus.
The membrane surrounding the cell is known as the cell wall, and in young plant cells is always composed of cellulose.
The granular substance lining the cell wall (Fig. 1, pr.) is called "protoplasm," and with the nucleus constitutes the living part of the cell. If sufficiently magnified, the granules within the protoplasm will be seen to be in active streaming motion. This movement, which is very evident here, is not often so conspicuous, but still may often be detected without difficulty.
The cell may be regarded as the unit of organic structure, and of cells are built up all of the complicated structures of which the bodies of the highest plants and animals are composed. We shall find that the cells may become very much modified for various purposes, but at first they are almost identical in structure, and essentially the same as the one we have just considered.
Very many of the lower forms of life consist of but a single cell which may occasionally be destitute of a cell wall. Such a form is shown in Figure 2. Here we have a mass of protoplasm with a nucleus (n) and cavities (vacuoles, v) filled with cell sap, but no cell wall. The protoplasm is in constant movement, and by extensions of a portion of the mass and contraction of other parts, the whole creeps slowly along. Other naked cells (Fig. 12, B; Fig. 16, C) are provided with delicate thread-like processes of protoplasm called "cilia" (sing. cilium), which are in active vibration, and propel the cell through the water.
On placing a cell into a fluid denser than the cell sap (e.g. a ten-per-cent solution of sugar in water), a portion of the water will be extracted from the cell, and we shall then see the protoplasm receding from the wall (Fig. 4, C), showing that it is normally in a state of tension due to pressure from within of the cell sap. The cell wall shows the same thing though in a less degree, owing to its being much more rigid than the protoplasmic lining. It is owing to the partial collapsing of the cells, consequent on loss of water, that plants wither when the supply of water is cut off.
As cells grow, new ones are formed in various ways. If the new cells remain together, cell aggregates, called tissues, are produced, and of these tissues are built up the various organs of the higher plants. The simplest tissues are rows of cells, such as form the hairs covering the surface of the organs of many flowering plants (Fig. 3), and are due to a division of the cells in a single direction. If the divisions take place in three planes, masses of cells, such as make up the stems, etc., of the higher plants, result (Fig. 4, A, B).
CLASSIFICATION OF PLANTS.—PROTOPHYTES.
For the sake of convenience it is desirable to collect into groups such plants as are evidently related; but as our knowledge of many forms is still very imperfect, any classification we may adopt must be to a great extent only provisional, and subject to change at any time, as new forms are discovered or others become better understood.
The following general divisions are usually accepted: I. Sub-kingdom (or Branch); II. Class; III. Order; IV. Family; V. Genus; VI. Species.
To illustrate: The white pine belongs to the highest great division (sub-kingdom) of the plant kingdom. The plants of this division all produce seeds, and hence are called "spermaphytes" ("seed plants"). They may be divided into two groups (classes), distinguished by certain peculiarities in the flowers and seeds. These are named respectively "gymnosperms" and "angiosperms," and to the first our plant belongs. The gymnosperms may be further divided into several subordinate groups (orders), one of which, the conifers, or cone-bearing evergreens, includes our plant. This order includes several families, among them the fir family (Abietineae), including the pines and firs. Of the sub-divisions (genera, sing. genus) of the fir family, one of the most familiar is the genus Pinus, which embraces all the true pines. Comparing different kinds of pines, we find that they differ in the form of the cones, arrangement of the leaves, and other minor particulars. The form we have selected differs from all other native forms in its cones, and also in having the leaves in fives, instead of twos or threes, as in most other kinds. Therefore to distinguish the white pine from all other pines, it is given a "specific" name, strobus.
The following table will show more plainly what is meant:
Sub-kingdom, Spermaphyta. /——————————^——————————- Includes all spermaphytes, or seed plants.
Class, Gymnospermae. /——————^—————— All naked-seeded plants.
Order, Coniferae. /———————^——————— All cone-bearing evergreens.
Family, Abietineae. /————^———— Firs, Pines, etc.
Genus, Pinus. /—-^—- Pines.
Species, Strobus. /——-^——- White Pine.
The name Protophytes (Protophyta) has been applied to a large number of simple plants, which differ a good deal among themselves. Some of them differ strikingly from the higher plants, and resemble so remarkably certain low forms of animal life as to be quite indistinguishable from them, at least in certain stages. Indeed, there are certain forms that are quite as much animal as vegetable in their attributes, and must be regarded as connecting the two kingdoms. Such forms are the slime moulds (Fig. 5), Euglena (Fig. 9), Volvox (Fig. 10), and others.
Other protophytes, while evidently enough of vegetable nature, are nevertheless very different in some respects from the higher plants.
The protophytes may be divided into three classes: I. The slime moulds (Myxomycetes); II. The Schizophytes; III. The green monads (Volvocineae).
CLASS I.—THE SLIME MOULDS.
These curious organisms are among the most puzzling forms with which the botanist has to do, as they are so much like some of the lowest forms of animal life as to be scarcely distinguishable from them, and indeed they are sometimes regarded as animals rather than plants. At certain stages they consist of naked masses of protoplasm of very considerable size, not infrequently several centimetres in diameter. These are met with on decaying logs in damp woods, on rotting leaves, and other decaying vegetable matter. The commonest ones are bright yellow or whitish, and form soft, slimy coverings over the substratum (Fig. 5, A), penetrating into its crevices and showing sensitiveness toward light. The plasmodium, as the mass of protoplasm is called, may be made to creep upon a slide in the following way: A tumbler is filled with water and placed in a saucer filled with sand. A strip of blotting paper about the width of the slide is now placed with one end in the water, the other hanging over the edge of the glass and against one side of a slide, which is thus held upright, but must not be allowed to touch the side of the tumbler. The strip of blotting paper sucks up the water, which flows slowly down the surface of the slide in contact with the blotting paper. If now a bit of the substance upon which the plasmodium is growing is placed against the bottom of the slide on the side where the stream of water is, the protoplasm will creep up against the current of water and spread over the slide, forming delicate threads in which most active streaming movements of the central granular protoplasm may be seen under the microscope, and the ends of the branches may be seen to push forward much as we saw in the amoeba. In order that the experiment may be successful, the whole apparatus should be carefully protected from the light, and allowed to stand for several hours. This power of movement, as well as the power to take in solid food, are eminently animal characteristics, though the former is common to many plants as well.
After a longer or shorter time the mass of protoplasm contracts and gathers into little heaps, each of which develops into a structure that has no resemblance to any animal, but would be at once placed with plants. In one common form (Trichia) these are round or pear-shaped bodies of a yellow color, and about as big as a pin head (Fig. 5, D), occurring in groups on rotten logs in damp woods. Others are stalked (Arcyria, Stemonitis) (Fig. 5, J, K), and of various colors,—red, brown, etc. The outer part of the structure is a more or less firm wall, which breaks when ripe, discharging a powdery mass, mixed in most forms with very fine fibres.
When strongly magnified the fine dust is found to be made up of innumerable small cells with thick walls, marked with ridges or processes which differ much in different species. The fibres also differ much in different genera. Sometimes they are simple, hair-like threads; in others they are hollow tubes with spiral thickenings, often very regularly placed, running around their walls.
The spores may sometimes be made to germinate by placing them in a drop of water, and allowing them to remain in a warm place for about twenty-four hours. If the experiment has been successful, at the end of this time the spore membrane will have burst, and the contents escaped in the form of a naked mass of protoplasm (Zooespore) with a nucleus, and often showing a vacuole (Fig. 5, v), that alternately becomes much distended, and then disappears entirely. On first escaping it is usually provided with a long, whip-like filament of protoplasm, which is in active movement, and by means of which the cell swims actively through the water (Fig. 5, I i). Sometimes such a cell will be seen to divide into two, the process taking but a short time, so that the numbers of these cells under favorable conditions may become very large. After a time the lash is withdrawn, and the cell assumes much the form of a small amoeba (I ii).
The succeeding stages are difficult to follow. After repeatedly dividing, a large number of these amoeba-like cells run together, coalescing when they come in contact, and forming a mass of protoplasm that grows, and finally assumes the form from which it started.
Of the common forms of slime moulds the species of Trichia (Figs. D, I) and Physarum are, perhaps, the best for studying the germination, as the spores are larger than in most other forms, and germinate more readily. The experiment is apt to be most successful if the spores are sown in a drop of water in which has been infused some vegetable matter, such as a bit of rotten wood, boiling thoroughly to kill all germs. A drop of this fluid should be placed on a perfectly clean cover glass, which it is well to pass once or twice through a flame, and the spores transferred to this drop with a needle previously heated. By these precautions foreign germs will be avoided, which otherwise may interfere seriously with the growth of the young slime moulds. After sowing the spores in the drop of culture fluid, the whole should be inverted over a so-called "moist chamber." This is simply a square of thick blotting paper, in which an opening is cut small enough to be entirely covered by the cover glass, but large enough so that the drop in the centre of the cover glass will not touch the sides of the chamber, but will hang suspended clear in it. The blotting paper should be soaked thoroughly in pure water (distilled water is preferable), and then placed on a slide, covering carefully with the cover glass with the suspended drop of fluid containing the spores. The whole should be kept under cover so as to prevent loss of water by evaporation. By this method the spores may be examined conveniently without disturbing them, and the whole may be kept as long as desired, so long as the blotting paper is kept wet, so as to prevent the suspended drop from drying up.
The Schizophytes are very small plants, though not infrequently occurring in masses of considerable size. They are among the commonest of all plants, and are found everywhere. They multiply almost entirely by simple transverse division, or splitting of the cells, whence their name. There are two pretty well-marked orders,—the blue-green slimes (Cyanophyceae) and the bacteria (Schizomycetes). They are distinguished, primarily, by the first (with a very few exceptions) containing chlorophyll (leaf-green), which is entirely absent from nearly all of the latter.
The blue-green slimes: These are, with few exceptions, green plants of simple structure, but possessing, in addition to the ordinary green pigment (chlorophyll, or leaf-green), another coloring matter, soluble in water, and usually blue in color, though sometimes yellowish or red.
As a representative of the group, we will select one of the commonest forms (Oscillaria), known sometimes as green slime, from forming a dark blue-green or blackish slimy coat over the mud at the bottom of stagnant or sluggish water, in watering troughs, on damp rocks, or even on moist earth. A search in the places mentioned can hardly fail to secure plenty of specimens for study. If a bit of the slimy mass is transferred to a china dish, or placed with considerable water on a piece of stiff paper, after a short time the edge of the mass will show numerous extremely fine filaments of a dark blue-green color, radiating in all directions from the mass (Fig. 6, a). The filaments are the individual plants, and possess considerable power of motion, as is shown by letting the mass remain undisturbed for a day or two, at the end of which time they will have formed a thin film over the surface of the vessel in which they are kept; and the radiating arrangement of the filaments can then be plainly seen.
If the mass is allowed to dry on the paper, it often leaves a bright blue stain, due to the blue pigment in the cells of the filament. This blue color can also be extracted by pulverizing a quantity of the dried plants, and pouring water over them, the water soon becoming tinged with a decided blue. If now the water containing the blue pigment is filtered, and the residue treated with alcohol, the latter will extract the chlorophyll, becoming colored of a yellow-green.
The microscope shows that the filaments of which the mass is composed (Fig. 6, B) are single rows of short cylindrical cells of uniform diameter, except at the end of the filament, where they usually become somewhat smaller, so that the tip is more or less distinctly pointed. The protoplasm of the cells has a few small granules scattered through it, and is colored uniformly of a pale blue-green. No nucleus can be seen.
If the filament is broken, there may generally be detected a delicate, colorless sheath that surrounds it, and extends beyond the end cells (Fig. 6, c). The filament increases in length by the individual cells undergoing division, this always taking place at right angles to the axis of the filament. New filaments are produced simply by the older ones breaking into a number of pieces, each of which rapidly grows to full size.
The name "oscillaria" arises from the peculiar oscillating or swinging movements that the plant exhibits. The most marked movement is a swaying from side to side, combined with a rotary motion of the free ends of the filaments, which are often twisted together like the strands of a rope. If the filaments are entirely free, they may often be observed to move forward with a slow, creeping movement. Just how these movements are caused is still a matter of controversy.
The lowest of the Cyanophyceae are strictly single-celled, separating as soon as formed, but cohering usually in masses or colonies by means of a thick mucilaginous substance that surrounds them (Fig. 7, D).
The higher ones are filaments, in which there may be considerable differentiation. These often occur in masses of considerable size, forming jelly-like lumps, which may be soft or quite firm (Fig. 7, A, B). They are sometimes found on damp ground, but more commonly attached to plants, stones, etc., in water. The masses vary in color from light brown to deep blackish green, and in size from that of a pin head to several centimetres in diameter.
In the higher forms special cells called heterocysts are found. They are colorless, or light yellowish, regularly disposed; but their function is not known. Besides these, certain cells become thick-walled, and form resting cells (spores) for the propagation of the plant (Fig. 7, C. sp.). In species where the sheath of the filament is well marked (Fig. 7, H), groups of cells slip out of the sheath, and develop a new one, thus giving rise to a new plant.
The bacteria (Schizomycetes), although among the commonest of organisms, owing to their excessive minuteness, are difficult to study, especially for the beginner. They resemble, in their general structure and methods of reproduction, the blue-green slimes, but are, with very few exceptions, destitute of chlorophyll, although often possessing bright pigments,—blue, violet, red, etc. It is one of these that sometimes forms blood-red spots in flour paste or bits of bread that have been kept very moist and warm. They are universally present where decomposition is going on, and are themselves the principal agents of decay, which is the result of their feeding upon the substance, as, like all plants without chlorophyll, they require organic matter for food. Most of the species are very tenacious of life, and may be completely dried up for a long time without dying, and on being placed in water will quickly revive. Being so extremely small, they are readily carried about in the air in their dried-up condition, and thus fall upon exposed bodies, setting up decomposition if the conditions are favorable.
A simple experiment to show this may be performed by taking two test tubes and partly filling them with an infusion of almost any organic substance (dried leaves or hay, or a bit of meat will answer). The fluid should now be boiled so as to kill any germs that may be in it; and while hot, one of the vessels should be securely stopped up with a plug of cotton wool, and the other left open. The cotton prevents access of all solid particles, but allows the air to enter. If proper care has been taken, the infusion in the closed vessel will remain unchanged indefinitely; but the other will soon become turbid, and a disagreeable odor will be given off. Microscopic examination shows the first to be free from germs of any kind, while the second is swarming with various forms of bacteria.
These little organisms have of late years attracted the attention of very many scientists, from the fact that to them is due many, if not all, contagious diseases. The germs of many such diseases have been isolated, and experiments prove beyond doubt that these are alone the causes of the diseases in question.
If a drop of water containing bacteria is examined, we find them to be excessively small, many of them barely visible with the strongest lenses. The larger ones (Fig. 8) recall quite strongly the smaller species of oscillaria, and exhibit similar movements. Others are so small as to appear as mere lines and dots, even with the strongest lenses. Among the common forms are small, nearly globular cells; oblong, rod-shaped or thread-shaped filaments, either straight or curved, or even spirally twisted. Frequently they show a quick movement which is probably in all cases due to cilia, which are, however, too small to be seen in most cases.
Reproduction is for the most part by simple transverse division, as in oscillaria; but occasionally spores are produced also.
CLASS III.—GREEN MONADS (Volvocineae).
This group of the protophytes is unquestionably closely related to certain low animals (Monads or Flagellata), with which they are sometimes united. They are characterized by being actively motile, and are either strictly unicellular, or the cells are united by a gelatinous envelope into a colony of definite form.
Of the first group, Euglena (Fig. 9), may be selected as a type.
This organism is found frequently among other algae, and occasionally forms a green film on stagnant water. It is sometimes regarded as a plant, sometimes as an animal, and is an elongated, somewhat worm-like cell without a definite cell wall, so that it can change its form to some extent. The protoplasm contains oval masses, which are bright green in color; but the forward pointed end of the cell is colorless, and has a little depression. At this end there is a long vibratile protoplasmic filament (c), by means of which the cell moves. There is also to be seen near this end a red speck (e) which is probably sensitive to light. A nucleus can usually be seen if the cell is first killed with an iodine solution, which often will render the flagellum (c) more evident, this being invisible while the cell is in motion. The cells multiply by division. Previous to this the flagellum is withdrawn, and a firm cell wall is formed about the cell (Fig. 9, B). The contents then divide into two or more parts, which afterwards escape as new individuals.
Of the forms that are united in colonies one of the best known is Volvox (Fig. 10). This plant is sometimes found in quiet water, where it floats on or near the surface as a dark green ball, just large enough to be seen with the naked eye. They may be kept for some time in aquaria, and will sometimes multiply rapidly, but are very susceptible to extremes of temperature, especially of heat.
 The term "colony" is, perhaps, inappropriate, as the whole mass of cells arises from a single one, and may properly be looked upon as an individual plant.
The colony (Fig. 10, A) is a hollow sphere, the numerous green cells of which it is composed forming a single layer on the outside. By killing with iodine, and using a strong lens, each cell is seen to be somewhat pear-shaped (Fig. B), with the pointed end out. Attached to this end are two vibratile filaments (cilia or flagella), and the united movements of these cause the rolling motion of the whole colony. Usually a number of young colonies (Fig. x) are found within the mother colony. These arise by the repeated bipartition of a single cell, and escape finally, forming independent colonies.
Another (sexual) form of reproduction occurs, similar to that found in many higher plants; but as it only occurs at certain seasons, it is not likely to be met with by the student.
Other forms related to Volvox, and sometimes met with, are Gonium, in which there are sixteen cells, forming a flat square; Pandorina and Eudorina, with sixteen cells, forming an oval or globular colony like Volvox, but much smaller. In all of these the structure of the cells is essentially as in Volvox.
 Algae (sing. alga).
In the second sub-kingdom of plants is embraced an enormous assemblage of plants, differing widely in size and complexity, and yet showing a sufficiently complete gradation from the lowest to the highest as to make it impracticable to make more than one sub-kingdom to include them. They are nearly all aquatic forms, although many of them will survive long periods of drying, such forms occurring on moist earth, rocks, or the trunks of trees, but only growing when there is a plentiful supply of water.
All of them possess chlorophyll, which, however, in many forms, is hidden by the presence of a brown or red pigment. They are ordinarily divided into three classes—I. The Green Algae (Chlorophyceae); II. Brown Algae (Phaeophyceae); III. Red Algae (Rhodophyceae).
CLASS I.—GREEN ALGAE.
The green algae are to be found almost everywhere where there is moisture, but are especially abundant in sluggish or stagnant fresh water, being much less common in salt water. They are for the most part plants of simple structure, many being unicellular, and very few of them plants of large size.
We may recognize five well-marked orders of the green algae—I. Green slimes (Protococcaceae); II. Confervaceae; III. Pond scums (Conjugatae); IV. Siphoneae; V. Stone-worts (Characeae).
The members of this order are minute unicellular plants, growing either in water or on the damp surfaces of stones, tree trunks, etc. The plants sometimes grow isolated, but usually the cells are united more or less regularly into colonies.
A common representative of the order is the common green slime, Protococcus (Fig. 11, A, C), which forms a dark green slimy coating over stones, tree trunks, flower pots, etc. Owing to their minute size the structure can only be made out with the microscope.
Scraping off a little of the material mentioned into a drop of water upon a slide, and carefully separating it with needles, a cover glass may be placed over the preparation, and it is ready for examination. When magnified, the green film is found to be composed of minute globular cells of varying size, which may in places be found to be united into groups. With a higher power, each cell (Fig. 11, A) is seen to have a distinct cell wall, within which is colorless protoplasm. Careful examination shows that the chlorophyll is confined to several roundish bodies that are not usually in immediate contact with the wall of the cell. These green masses are called chlorophyll bodies (chloroplasts). Toward the centre of the cell, especially if it has first been treated with iodine, the nucleus may be found. The size of the cells, as well as the number of chloroplasts, varies a good deal.
With a little hunting, specimens in various stages of division may be found. The division takes place in two ways. In the first (Fig. 11, B), known as fission, a wall is formed across the cell, dividing it into two cells, which may separate immediately or may remain united until they have undergone further division. In this case the original cell wall remains as part of the wall of the daughter cells. Fission is the commonest form of cell multiplication throughout the vegetable kingdom.
The second form of cell division or internal cell division is shown at C. Here the protoplasm and nucleus repeatedly divide until a number of small cells are formed within the old one. These develop cell walls, and escape by the breaking of the old cell wall, which is left behind, and takes no part in the process. The cells thus formed are sometimes provided with two cilia, and are capable of active movement.
Internal cell division, as we shall see, is found in most plants, but only at special times.
Closely resembling Protococcus, and answering quite as well for study, are numerous aquatic forms, such as Chlorococcum (Fig. 12). These are for the most part destitute of a firm cell wall, but are imbedded in masses of gelatinous substance like many Cyanophyceae. The chloroplasts are smaller and less distinct than in Protococcus. The cells are here oval rather than round, and often show a clear space at one end.
Owing to the absence of a definite membrane, a distinction between fission and internal cell division can scarcely be made here. Often the cells escape from the gelatinous envelope, and swim actively by means of two cilia at the colorless end (Fig. 12, B). In this stage they closely resemble the individuals of a Volvox colony, or other green Flagellata, to which there is little doubt that they are related.
There are a number of curious forms common in fresh water that are probably related to Protococcus, but differ in having the cells united in colonies of definite form. Among the most striking are the different species of Pediastrum (Fig. 11, D, E), often met with in company with other algae, and growing readily in aquaria when once established. They are of very elegant shapes, and the number of cells some multiple of four, usually sixteen.
The cells form a flat disc, the outer ones being generally provided with a pair of spines.
New individuals arise by internal division of the cells, the contents of each forming as many parts as there are cells in the whole colony. The young cells now escape through a cleft in the wall of the mother cell, but are still surrounded by a delicate membrane (Fig. 11, E). Within this membrane the young cells arrange themselves in the form of the original colony, and grow together, forming a new colony.
A much larger but rarer form is the water net (Fig. 11, G), in which the colony has the form of a hollow net, the spaces being surrounded by long cylindrical cells placed end to end. Other common forms belong to the genus Scenedesmus (Fig. 11, F), of which there are many species.
Under this head are included a number of forms of which the simplest ones approach closely, especially in their younger stages, the Protococcaceae. Indeed, some of the so-called Protococcaceae are known to be only the early stages of these plants.
A common member of this order is Cladophora, a coarse-branching alga, growing commonly in running water, where it forms tufts, sometimes a metre or more in length. By floating out a little of it in a saucer, it is easy to see that it is made up of branching filaments.
The microscope shows (Fig. 13, A) that these filaments are rows of cylindrical cells with thick walls showing evident stratification. At intervals branches are given off, which may in turn branch, giving rise to a complicated branching system. These branches begin as little protuberances of the cell wall at the top of the cell. They increase rapidly in length, and becoming slightly contracted at the base, a wall is formed across at this point, shutting it off from the mother cell.
The protoplasm lines the wall of the cell, and extends in the form of thin plates across the cavity of the cell, dividing it up into a number of irregular chambers. Imbedded in the protoplasm are numerous flattened chloroplasts, which are so close together as to make the protoplasm appear almost uniformly green. Within the chloroplasts are globular, glistening bodies, called "pyrenoids." The cell has several nuclei, but they are scarcely evident in the living cell. By placing the cells for a few hours in a one per cent watery solution of chromic acid, then washing thoroughly and staining with borax carmine, the nuclei will be made very evident (Fig. 13, B). Such preparations may be kept permanently in dilute glycerine.
If a mass of actively growing filaments is examined, some of the cells will probably be found in process of fission. The process is very simple, and may be easily followed (Fig. 13, C). A ridge of cellulose is formed around the cell wall, projecting inward, and pushing in the protoplasm as it grows. The process is continued until the ring closes in the middle, cutting the protoplasmic body completely in two, and forms a firm membrane across the middle of the cell. The protoplasm at this stage (C iii.) is somewhat contracted, but soon becomes closely applied to the new wall. The whole process lasts, at ordinary temperatures (20 deg.-25 deg. C.), from three to four hours.
At certain times, but unfortunately not often to be met with, the contents of some of the cells form, by internal division, a large number of small, naked cells (zooespores) (Fig. 13, D), which escape and swim about actively for a time, and afterwards become invested with a cell wall, and grow into a new filament. These cells are called zooespores, from their animal-like movements. They are provided with two cilia, closely resembling the motile cells of the Protococcaceae and Volvocineae.
There are very many examples of these simple Confervaceae, some like Conferva being simple rows of cells, others like Stigeoclonium (Fig. 14, A), Chaetophora and Draparnaldia (Fig. 14, B, C), very much branched. The two latter forms are surrounded by masses of transparent jelly, which sometimes reach a length of several centimetres.
Among the marine forms related to these may be mentioned the sea lettuce (Ulva), shown in Figure 15. The thin, bright-green, leaf-like fronds of this plant are familiar to every seaside student.
Somewhat higher than Cladophora and its allies, especially in the differentiation of the reproductive parts, are the various species of OEdogonium and its relatives. There are numerous species of OEdogonium not uncommon in stagnant water growing in company with other algae, but seldom forming masses by themselves of sufficient size to be recognizable to the naked eye.
The plant is in structure much like Cladophora, except that it is unbranched, and the cells have but a single nucleus (Fig. 16, E). Even when not fruiting the filaments may usually be recognized by peculiar cap-shaped structures at the top of some of the cells. These arise as the result of certain peculiarities in the process of cell division, which are too complicated to be explained here.
There are two forms of reproduction, non-sexual and sexual. In the first the contents of certain cells escape in the form of large zooespores (Fig. 16, C), of oval form, having the smaller end colorless and surrounded by a crown of cilia. After a short period of active motion, the zooespore comes to rest, secretes a cell wall about itself, and the transparent end becomes flattened out into a disc (E, d), by which it fastens itself to some object in the water. The upper part now rapidly elongates, and dividing repeatedly by cross walls, develops into a filament like the original one. In many species special zooespores are formed, smaller than the ordinary ones, that attach themselves to the filaments bearing the female reproductive organ (ooegonium), and grow into small plants bearing the male organ (antheridium), (Fig. 16, B).
The sexual reproduction takes place as follows: Certain cells of a filament become distinguished by their denser contents and by an increase in size, becoming oval or nearly globular in form (Fig. 16, A, B). When fully grown, the contents contract and form a naked cell, which sometimes shows a clear area at one point on the surface. This globular mass of protoplasm is the egg cell, or female cell, and the cell containing it is called the "ooegonium." When the egg cell is ripe, the ooegonium opens by means of a little pore at one side (Fig. 16, A).
In other cells, either of the same filament or else of the small male plants already mentioned, small motile cells, called spermatozoids, are formed. These are much smaller than the egg cell, and resemble the zooespores in form, but are much smaller, and without chlorophyll. When ripe they are discharged from the cells in which they were formed, and enter the ooegonium. By careful observation the student may possibly be able to follow the spermatozoid into the ooegonium, where it enters the egg cell at the clear spot on its surface. As a result of the entrance of the spermatozoid (fertilization), the egg cell becomes surrounded by a thick brown wall, and becomes a resting spore. The spore loses its green color, and the wall becomes dark colored and differentiated into several layers, the outer one often provided with spines (Fig. 16, F). As these spores do not germinate for a long time, the process is only known in a comparatively small number of species, and can hardly be followed by the ordinary student.
Much like OEdogonium, but differing in being branched, is the genus Bulbochaete, characterized also by hairs swollen at the base, and prolonged into a delicate filament (Fig. 16, G).
The highest members of the Confervaceae are those of the genus Coleochaete (Fig. 17), of which there are several species found in the United States. These show some striking resemblances to the red seaweeds, and possibly form a transition from the green algae to the red. The commonest species form bright-green discs, adhering firmly to the stems and floating leaves of water lilies and other aquatics. In aquaria they sometimes attach themselves in large numbers to the glass sides of the vessel.
Growing from the upper surface are numerous hairs, consisting of a short, sheath-like base, including a very long and delicate filament (Fig. 17, B). In their methods of reproduction they resemble OEdogonium, but the reproductive organs are more specialized.
ORDER III.—POND SCUMS (Conjugatae).
The Conjugatae, while in some respects approaching the Confervaceae in structure, yet differ from them to such an extent in some respects that their close relationship is doubtful. They are very common and familiar plants, some of them forming great floating masses upon the surface of every stagnant pond and ditch, being commonly known as "pond scum." The commonest of these pond scums belong to the genus Spirogyra, and one of these will illustrate the characteristics of the order. When in active growth these masses are of a vivid green, and owing to the presence of a gelatinous coating feel slimy, slipping through the hands when one attempts to lift them from the water. Spread out in water, the masses are seen to be composed of slender threads, often many centimetres in length, and showing no sign of branching.
For microscopical examination the larger species are preferable. When one of these is magnified (Fig. 18, A, C), the unbranched filament is shown to be made up of perfectly cylindrical cells, with rather delicate walls. The protoplasm is confined to a thin layer lining the walls, except for numerous fine filaments that radiate from the centrally placed nucleus (n), which thus appears suspended in the middle of the cell. The nucleus is large and distinct in the larger species, and has a noticeably large and conspicuous nucleolus. The most noticeable thing about the cell is the green spiral bands running around it. These are the chloroplasts, which in all the Conjugatae are of very peculiar forms. The number of these bands varies much in different species of Spirogyra, but is commonly two or three. These chloroplasts, like those of other plants, are not noticeably different in structure from the ordinary protoplasm, as is shown by extracting the chlorophyll, which may be done by placing the plants in alcohol for a short time. This extracts the chlorophyll, but a microscopic examination of the decolored cells shows that the bands remain unchanged, except for the absence of color. These bands are flattened, with irregularly scalloped margins, and at intervals have rounded bodies (pyrenoids) imbedded in them (Fig. 18, C, py.). The pyrenoids, especially when the plant has been exposed to the light for some time, are surrounded by a circle of small granules, which become bluish when iodine is applied, showing them to be starch. (To show the effect of iodine on starch on a large scale, mix a little flour, which is nearly all starch, with water, and add a little iodine. The starch will immediately become colored blue, varying in intensity with the amount of iodine.) The cells divide much as in Cladophora, but the nucleus here takes part in the process. The division naturally occurs only at night, but by reducing the temperature at night to near the freezing point (4 deg. C., or a little lower), the process may be checked. The experiment is most conveniently made when the temperature out of doors approaches the freezing point. Then it is only necessary to keep the plants in a warm room until about 10 P.M., when they may be put out of doors for the night. On bringing them in in the morning, the division will begin almost at once, and may be easily studied. The nucleus divides into two parts, which remain for a time connected by delicate threads (Fig. 18, B), that finally disappear. At first no nucleoli are present in the daughter nuclei, but they appear before the division is complete.
New filaments are formed by the breaking up of the old ones, this sometimes being very rapid. As the cells break apart, the free ends bulge strongly, showing the pressure exerted upon the cell wall by the contents (Fig. 18, A).
Spores like those of OEdogonium are formed, but the process is somewhat different. It occurs in most species late in the spring, but may sometimes be met with at other times. The masses of fruiting plants usually appear brownish colored. If spores have been formed they can, in the larger species at least, be seen with a hand lens, appearing as rows of dark-colored specks.
Two filaments lying side by side send out protuberances of the cell wall that grow toward each other until they touch (Fig. 18, D). At the point of contact, the wall is absorbed, forming a continuous channel from one cell to the other. This process usually takes place in all the cells of the two filaments, so that the two filaments, connected by tubes at regular intervals, have the form of a ladder.
In some species adjoining cells of the same filament become connected, the tubes being formed at the end of the cells (Fig. 18, H), and the cell in which the spore is formed enlarges.
Soon after the channel is completed, the contents of one cell flow slowly through it into the neighboring cell, and the protoplasm of the two fuses into one mass. (The union of the nuclei has also been observed.) The young spore thus formed contracts somewhat, becoming oval in form, and soon secretes a thick wall, colorless at first, but afterwards becoming brown and more or less opaque. The chlorophyll bands, although much crowded, are at first distinguishable, but later lose the chlorophyll, and become unrecognizable. Like the resting spores of OEdogonium these require a long period of rest before germinating.
There are various genera of the pond scums, differing in the form of the chloroplasts and also in the position of the spores. Of these may be mentioned Zygnema (Fig. 19, A), with two star-shaped chloroplasts in each cell, and Mesocarpus (Fig. 19, B, D), in which the single chloroplast has the form of a thin median plate. (B shows the appearance from in front, C from the side, showing the thickness of the plate.) Mesocarpus and the allied genera have the spore formed between the filaments, the contents of both the uniting cells leaving them.
Evidently related to the pond scums, but differing in being for the most part strictly unicellular, are the desmids (Fig. 20). They are confined to fresh water, and seldom occur in masses of sufficient size to be seen with the naked eye, usually being found associated with pond scums or other filamentous forms. Many of the most beautiful forms may be obtained by examining the matter adhering to the leaves and stems of many floating water plants, especially the bladder weed (Utricularia) and other fine-leaved aquatics.
The desmids include the most beautiful examples of unicellular plants to be met with, the cells having extremely elegant outlines. The cell shows a division into two parts, and is often constricted in the middle, each division having a single large chloroplast of peculiar form. The central part of the cell in which the nucleus lies is colorless.
Among the commonest forms, often growing with Spirogyra, are various species of Closterium (Fig. 20, A, B), recognizable at once by their crescent shape. The cell appears bright green, except at the ends and in the middle. The large chloroplast in each half is composed of six longitudinal plates, united at the axis of the cell. Several large pyrenoids are always found, often forming a regular line through the central axis. At each end of the cell is a vacuole containing small granules that show an active dancing movement.
The desmids often have the power of movement, swimming or creeping slowly over the slide as we examine them, but the mechanism of these movements is still doubtful.
In their reproduction they closely resemble the pond scums.
The Siphoneae are algae occurring both in fresh and salt water, and are distinguished from other algae by having the form of a tube, undivided by partition walls, except when reproduction occurs. The only common representatives of the order in fresh water are those belonging to the genus Vaucheria, but these are to be had almost everywhere. They usually occur in shallow ditches and ponds, growing on the bottom, or not infrequently becoming free, and floating where the water is deeper. They form large, dark green, felted masses, and are sometimes known as "green felts." Some species grow also on the wet ground about springs. An examination of one of the masses shows it to be made up of closely matted, hair-like threads, each of which is an individual plant.
In transferring the plants to the slide for microscopic examination, they must be handled very carefully, as they are very easily injured. Each thread is a long tube, branching sometimes, but not divided into cells as in Spirogyra or Cladophora. If we follow it to the tip, the contents here will be found to be denser, this being the growing point. By careful focusing it is easy to show that the protoplasm is confined to a thin layer lining the wall, the central cavity of the tube being filled with cell sap. In the protoplasm are numerous elongated chloroplasts (cl.). and a larger or smaller number of small, shining, globular bodies (ol.). These latter are drops of oil, and, when the filaments are injured, sometimes run together, and form drops of large size. No nucleus can be seen in the living plant, but by treatment with chromic acid and staining, numerous very small nuclei may be demonstrated.
When the filaments are growing upon the ground, or at the bottom of shallow water, the lower end is colorless, and forms a more or less branching root-like structure, fastening it to the earth. These rootlets, like the rest of the filament, are undivided by walls.
One of the commonest and at the same time most characteristic species is Vaucheria racemosa (Fig. 21, A, F). The plant multiplies non-sexually by branches pinched off by a constriction at the point where they join the main filament, or by the filament itself becoming constricted and separating into several parts, each one constituting a new individual.
The sexual organs are formed on special branches, and their arrangement is such as to make the species instantly recognizable.
The first sign of their development is the formation of a short branch (Fig. 21, A) growing out at right angles to the main filament. This branch becomes club-shaped, and the end somewhat pointed and more slender, and curves over. This slender, curved portion is almost colorless, and is soon shut off from the rest of the branch. It is called an "antheridium," and within are produced, by internal division, numerous excessively small spermatozoids.
As the branch grows, its contents become very dense, the oil drops especially increasing in number and size. About the time that the antheridium becomes shut off, a circle of buds appears about its base (Fig. 21, B, og.). These are the young ooegonia, which rapidly increase in size, assuming an oval form, and become separated by walls from the main branch (C). Unlike the antheridium, the ooegonia contain a great deal of chlorophyll, appearing deep green.
When ripe, the antheridium opens at the end and discharges the spermatozoids, which are, however, so very small as scarcely to be visible except with the strongest lenses. They are little oval bodies with two cilia, which may sometimes be rendered visible by staining with iodine.
The ooegonia, which at first are uniformly colored, just before maturity show a colorless space at the top, from which the chloroplasts and oil drops have disappeared (D), and at the same time this portion pushes out in the form of a short beak. Soon after the wall is absorbed at this point, and a portion of the contents is forced out, leaving an opening, and at the same time the remaining contents contract to form a round mass, the germ or egg cell (Fig. 21, E, o). Almost as soon as the ooegonium opens, the spermatozoids collect about it and enter; but, on account of their minuteness, it is almost impossible to follow them into the egg cell, or to determine whether several or only one enter. The fertilized egg cell becomes almost at once surrounded by a wall, which rapidly thickens, and forms a resting spore. As the spore ripens, it loses its green color, becoming colorless, with a few reddish brown specks scattered through it (F).
In some species the sexual organs are borne directly on the filament (Fig. 21, G).
Large zooespores are formed in some of the green felts (Fig. 22, A), and are produced singly in the ends of branches that become swollen, dark green, and filled with very dense protoplasm. This end becomes separated by a wall from the rest of the branch, the end opens, and the contents escape as a very large zooespore, covered with numerous short cilia (A ii). After a short period of activity, this loses its cilia, develops a wall, and begins to grow (III, IV). Other species (B) produce similar spores, which, however, are not motile, and remain within the mother cell until they are set free by the decay of its wall.
The Characeae, or stone-worts, as some of them are called, are so very different from the other green algae that it is highly probable that they should be separated from them.
The type of the order is the genus Chara (Fig. 23), called stone-worts from the coating of carbonate of lime found in most of them, giving them a harsh, stony texture. Several species are common growing upon the bottom of ponds and slow streams, and range in size from a few centimetres to a metre or more in height.
The plant (Fig. 23, A) consists of a central jointed axis with circles of leaves at each joint or node. The distance between the nodes (internodes) may in the larger species reach a length of several centimetres. The leaves are slender, cylindrical structures, and like the stem divided into nodes and internodes, and have at the nodes delicate leaflets.
At each joint of the leaf, in fruiting specimens, attached to the inner side, are borne two small, roundish bodies, in the commoner species of a reddish color (Fig. 23, A, r). The lower of the two is globular, and bright scarlet in color; the other, more oval and duller.
Examined with a lens the main axis presents a striated appearance. The whole plant is harsh to the touch and brittle, owing to the limy coating. It is fastened to the ground by fine, colorless hairs, or rootlets.
[Illustration: FIG. 23.—A, plant of a stone-wort (Chara), one-half natural size. r, reproductive organs. B, longitudinal section through the apex. S, apical cell. x, nodes. y, internodes. C, a young leaf. D, cross section of an internode. E, of a node of a somewhat older leaf. F, G, young sexual organs seen in optical section. o, ooegonium. An. antheridium. H, superficial view. G, I, group of filaments containing spermatozoids. J, a small portion of one of these more magnified, showing a spermatozoid in each cell. K, free spermatozoids. L, a piece of a leaf with ripe ooegonium (o), and antheridium (An.). B, H, x 150. J, K, x 300. I, x 50. L, x 25.]
By making a series of longitudinal sections with a sharp razor through the top of the plant, and magnifying sufficiently, it is found to end in a single, nearly hemispherical cell (Fig. 23, B, S). This from its position is called the "apical cell," and from it are derived all the tissues of the plant. Segments are cut off from its base, and these divide again into two by a wall parallel to the first. Of the two cells thus formed one undergoes no further division and forms the central cell of an internode (y); the other divides repeatedly, forming a node or joint (x).
As the arrangement of these cells is essentially the same in the leaves and stem, we will examine it in the former, as by cutting several cross-sections of the whole bunch of young leaves near the top of the plant, we shall pretty certainly get some sections through a joint. The arrangement is shown in Figure 23, E.
As the stem grows, a covering is formed over the large internodal cell (y) by the growth of cells from the nodes. These grow both from above and below, meeting in the middle of the internode and completely hiding the long axial cell. A section across the internode shows the large axial cell (y) surrounded by the regularly arranged cells of the covering or cortex (Fig. 23, D).
All the cells contain a layer of protoplasm next the wall with numerous oval chloroplasts. If the cells are uninjured, they often show a very marked movement of the protoplasm. These movements are best seen, however, in forms like Nitella, where the long internodal cells are not covered with a cortex. In Chara they are most evident in the root hairs that fasten the plant to the ground.
The growth of the leaves is almost identical with that of the stem, but the apical growth is limited, and the apical cell becomes finally very long and pointed (Fig. 23, C). In some species the chloroplasts are reddish in the young cells, assuming their green color as the cells approach maturity.
The plant multiplies non-sexually by means of special branches that may become detached, but there are no non-sexual spores formed.
The sexual organs have already been noticed arising in pairs at the joints of the leaves. The ooegonium is formed above, the antheridium below.
The young ooegonium (F, O) consists of a central cell, below which is a smaller one surrounded by a circle of five others, which do not at first project above the central cell, but later completely envelop it (G). Each of these five cells early becomes divided into an upper and a lower one, the latter becoming twisted as it elongates, and the central cell later has a small cell cut off from its base by an oblique wall. The central cell forms the egg cell, which in the ripe ooegonium (L, O) is surrounded by five, spirally twisted cells, and crowned by a circle of five smaller ones, which become of a yellowish color when full grown. They separate at the time of fertilization to allow the spermatozoids to enter the ooegonium.
The antheridium consists at first of a basal cell and a terminal one. The latter, which is nearly globular, divides into eight nearly similar cells by walls passing through the centre. In each of these eight cells two walls are next formed parallel to the outer surface, so that the antheridium (apart from the basal cell) contains twenty-four cells arranged in three concentric series (G, an.). These cells, especially the outer ones, develop a great amount of a red pigment, giving the antheridium its characteristic color.
The diameter of the antheridium now increases rapidly, and the central cells separate, leaving a large space within. Of the inner cells, the second series, while not increasing in diameter, elongate, assuming an oblong form, and from the innermost are developed long filaments (I, J) composed of a single row of cells, in each of which is formed a spermatozoid.
The eight outer cells are nearly triangular in outline, fitting together by deeply indented margins, and having the oblong cells with the attached filaments upon their inner faces.
If a ripe antheridium is crushed in a drop of water, after lying a few minutes the spermatozoids will escape through small openings in the side of the cells. They are much larger than any we have met with. Each is a colorless, spiral thread with about three coils, one end being somewhat dilated with a few granules; the other more pointed, and bearing two extremely long and delicate cilia (K). To see the cilia it is necessary to kill the spermatozoids with iodine or some other reagent.
After fertilization the outer cells of the ooegonium become very hard, and the whole falls off, germinating after a sufficient period of rest.
According to the accounts of Pringsheim and others, the young plant consists at first of a row of elongated cells, upon which a bud is formed that develops into the perfect plant.
There are two families of the Characeae, the Chareae, of which Chara is the type, and the Nitelleae, represented by various species of Nitella and Tolypella. The second family have the internodes without any cortex—that is, consisting of a single long cell; and the crown at the top of the ooegonium is composed of ten cells instead of five. They are also destitute of the limy coating of the Chareae.
Both as regards the structure of the plant itself, as well as the reproductive organs, especially the very complex antheridium, the Characeae are very widely separated from any other group of plants, either above or below them.
THE BROWN ALGAE (Phaeophyceae).
These plants are all characterized by the presence of a brown pigment, in addition to the chlorophyll, which almost entirely conceals the latter, giving the plants a brownish color, ranging from a light yellowish brown to nearly black. One order of plants that possibly belongs here (Diatomaceae) are single celled, but the others are for the most part large seaweeds. The diatoms, which are placed in this class simply on account of the color, are probably not closely related to the other brown algae, but just where they should be placed is difficult to say. In some respects they approach quite closely the desmids, and are not infrequently regarded as related to them. They are among the commonest of organisms occurring everywhere in stagnant and running water, both fresh and salt, forming usually, slimy, yellowish coatings on stones, mud, aquatic plants, etc. Like the desmids they may be single or united into filaments, and not infrequently are attached by means of a delicate gelatinous stalk (Fig. 25).
They are at once distinguished from the desmids by their color, which is always some shade of yellowish or reddish brown. The commonest forms, e.g. Navicula (Fig. 24, C), are boat-shaped when seen from above, but there is great variety in this respect. The cell wall is always impregnated with large amounts of flint, so that after the cell dies its shape is perfectly preserved, the flint making a perfect cast of it, looking like glass. These flinty shells exhibit wonderfully beautiful and delicate markings which are sometimes so fine as to test the best lenses to make them out.
This shell is composed of two parts, one shutting over the other like a pill box and its cover. This arrangement is best seen in such large forms as Pinnularia (Fig. 24, A ii).
Most of the diatoms show movements, swimming slowly or gliding over solid substances; but like the movements of Oscillaria and the desmids, the movements are not satisfactorily understood, although several explanations have been offered.
They resemble somewhat the desmids in their reproduction.
THE TRUE BROWN ALGAE.
These are all marine forms, many of great size, reaching a length in some cases of a hundred metres or more, and showing a good deal of differentiation in their tissues and organs.
One of the commonest forms is the ordinary rock weed (Fucus), which covers the rocks of our northeastern coast with a heavy drapery for several feet above low-water mark, so that the plants are completely exposed as the tide recedes. The commonest species, F. vesiculosus (Fig. 26, A), is distinguished by the air sacs with which the stems are provided. The plant is attached to the rock by means of a sort of disc or root from which springs a stem of tough, leathery texture, and forking regularly at intervals, so that the ultimate branches are very numerous, and the plant may reach a length of a metre or more. The branches are flattened and leaf-like, the centre traversed by a thickened midrib. The end of the growing branches is occupied by a transversely elongated pit or depression. The growing point is at the bottom of this pit, and by a regular forking of the growing point the symmetrical branching of the plant is brought about. Scattered over the surface are little circular pits through whose openings protrude bunches of fine hairs. When wet the plant is flexible and leathery, but it may become quite dry and hard without suffering, as may be seen when the plants are exposed to the sun at low tide.
The air bladders are placed in pairs, for the most part, and buoy up the plant, bringing it up to the surface when covered with water.
The interior of the plant is very soft and gelatinous, while the outer part forms a sort of tough rind of much firmer consistence. The ends of some of the branches (Fig. 26, A, x) are usually much swollen, and the surface covered with little elevations from which may often be seen protruding clusters of hairs like those arising from the other parts of the plant. A section through one of these enlarged ends shows that each elevation corresponds to a cavity situated below it. On some of the plants these cavities are filled with an orange-yellow mass; in others there are a number of roundish olive-brown bodies large enough to be easily seen. The yellow masses are masses of antheridia; the round bodies, the ooegonia.
If the plants are gathered while wet, and packed so as to prevent evaporation of the water, they will keep perfectly for several days, and may readily be shipped for long distances. If they are to be studied away from the seashore, sections for microscopic examination should be mounted in salt water (about 3 parts in weight of common salt to 100 of water). If fresh material is not to be had, dried specimens or alcoholic material will answer pretty well.
To study the minute structure of the plant, make a thin cross-section, and mount in salt water. The inner part or pith is composed of loosely arranged, elongated cells, placed end to end, and forming an irregular network, the large spaces between filled with the mucilaginous substance derived from the altered outer walls of these cells. This mucilage is hard when dry, but swells up enormously in water, especially fresh water. The cells grow smaller and more compact toward the outside of the section, until there are no spaces of any size between those of the outside or rind. The cells contain small chloroplasts like those of the higher plants, but owing to the presence of the brown pigment found in all of the class, in addition to the chlorophyll, they appear golden brown instead of green.
No non-sexual reproductive bodies are known in the rock weeds, beyond small branches that occur in clusters on the margins of the main branches, and probably become detached, forming new plants. In some of the lower forms, however, e.g. Ectocarpus and Laminaria (Fig. 28, A, C), zooespores are formed.
The sexual organs of the rock weed, as we have already seen, are borne in special cavities (conceptacles) in the enlarged ends of some of the branches. In the species here figured, F. vesiculosus, the antheridia and ooegonia are borne on separate plants; but in others, e.g. F. platycarpus, they are both in the same conceptacle.
The walls of the conceptacle (Fig. 26, B) are composed of closely interwoven filaments, from which grow inward numerous hairs, filling up the space within, and often extending out through the opening at the top.
The reproductive bodies arise from the base of these hairs. The ooegonia (Fig. 26, C, E) arise as nearly colorless cells, that early become divided into two cells, a short basal cell or stalk and a larger terminal one, the ooegonium proper. The latter enlarges rapidly, and its contents divide into eight parts. The division is at first indicated by a division of the central portion, which includes the nucleus, and is colored brown, into two, four, and finally eight parts, after which walls are formed between these. The brown color spreads until the whole ooegonium is of a nearly uniform olive-brown tint.
When ripe, the upper part of the ooegonium dissolves, allowing the eight cells, still enclosed in a delicate membrane, to escape (Fig. 27, H). Finally, the walls separating the inner cells of the ooegonium become also absorbed, as well as the surrounding membrane, and the eight egg cells escape into the water (Fig. 27, I) as naked balls of protoplasm, in which a central nucleus may be dimly seen.
The antheridia (Fig. 26, F, G) are small oblong cells, at first colorless, but when ripe containing numerous glistening, reddish brown dots, each of which is part of a spermatozoid. When ripe, the contents of the antheridium are forced out into the water (G), leaving the empty outer wall behind, but still surrounded by a thin membrane. After a few minutes this membrane is dissolved, and the spermatozoids are set free. These (Fig. 27, K) are oval in form, with two long cilia attached to the side where the brown speck, seen while still within the antheridium, is conspicuous.
The act of fertilization may be easily observed by laying fresh antheridia into a drop of water containing recently discharged egg cells. To obtain these, all that is necessary is to allow freshly gathered plants to remain in the air until they are somewhat dry, when the ripe sexual cells will be discharged from the openings of the conceptacles, exuding as little drops, those with antheridia being orange-yellow; the masses of ooegonia, olive. Within a few minutes after putting the ooegonia into water, the egg cells may be seen to escape into the water, when some of the antheridia may be added. The spermatozoids will be quickly discharged, and collect immediately in great numbers about the egg cells, to which they apply themselves closely, often setting them in rotation by the movements of their cilia, and presenting a most extraordinary spectacle (J). Owing to the small size of the spermatozoids, and the opacity of the eggs, it is impossible to see whether more than one spermatozoid penetrates it; but from what is known in other cases it is not likely. The egg now secretes a wall about itself, and within a short time begins to grow. It becomes pear-shaped, the narrow portion becoming attached to the parent plant or to some other object by means of rootlets, and the upper part grows into the body of the young plant (Fig. 27, M).