Outlines of plant life : with special reference to form and function

Introduction

1. Living matter. — By the combination of powers called life, each living thing controls, for a longer or shorter time, a certain amount of material, which constitutes its body. This material is arranged into definite form ; some remains only for a short time as part of the body and is then discarded; other material remains part of the body as long as life exists.

That which is changing most rapidly is the living substance, called protoplasm. If there are parts of the body not living, they have been formed by the protoplasm and are generally controlled by it.

2. Members. — When the body is large, it is easy to see that it is made up of more or less distinct parts. These are its members. As a rule, the smaller it is, the fewer and less distinct are the members. There are many thousands of plants in which the body does not have any members, but can be distinguished only into the units of which it is built, called cells. Still others consist of a single cell.

In the largest plants the more important members may be divisible into smaller subordinate ones. When these are inspected they too are seen to be made up of a great many minute parts, each consisting of a bit of living protoplasm and some other things which it has made. These parts are called cells. (See ^[ 4.)

Thus, a corn plant has two principal members, a root, below ground, and a shoot above ground. The root consists of many subordinate members, the roots and the rootlets; the shoot consists of stem and leaves ; the leaves of sheath and blade, etc. But a duckweed shoot has no distinction of stem and leaf, and only a single root. The pond scums have no members, but consist of a row of cells; while in many diatoms the body is a single cell.

3. Reproduction. — Every plant must provide for its own existence. To do this, it must possess means for securing, or for making, and using food. During this feeding period its most striking characteristic is growth. It must also provide before it dies for the production of new plants of the same kind. When the plant is very simple, both duties must be done by the same cell, but in more complex plants special cells, and in many cases special members, are provided for reproduction. The two processes are sometimes carried on at the same time, but more commonly reproduction occurs at some particular or limited period.

It is convenient to consider first the form of the plant body and those members which are not concerned in reproduction. Parts I and II therefore, treat of the work and parts of the plant which promote its own life and growth, i.e. the vegetative body. Part III discusses the form and action of the reproductive parts, so far as these can be studied without a microscope.

4. The cell. — A plant-cell is a minute portion of living matter, called protoplasm, generally surrounded by a membrane, called the cell-wall (fig. 1).

The protoplasm is the essential part of the cell. It constructs the cell-wall. Rarely, if ever, is it uniform through-

INTAOD UCTION.

out, but shows distinct parts, each having special work to do. In the most complete and active cells the greater part of the protoplasm consists of a finely granular or nearly transparent, colorless portion, in which the other parts seem embedded.

Protoplasm is not a single substance, but a mixture of several different substances, so intimately mixed and so easily destroyed that it is not possible to analyze it. Moreover, the nature and amount of the components are probably variable.

In all but the youngest cells there are one or more bubbles of water in the protoplasm.

5. Nucleus. — The nucleus is one of the most important parts of the cell. It is generally spherical or ovoid, but in long cells it may become elongated (fig. 2, z). The nucleus may divide into two, and this is commonly followed by the formation of a partition-wall separating the cell into two parts, each containing one of the daughter-nuclei.

6. Plastids. — In most cells there are also other parts, called plastids. In young cells these are small, rounded, colorless bodies. As the cell grows older they increase in size and number. When mature and in cells which lie near the surface of green plants, they are commonly roundish or biscuit-shaped, of spongy texture, and colored yelllowishgreen by a substance known as chlorophyll . These are consequently known as chloroplasts or chlorophyll-bodies (fig. 2). In other cells, particularly those for the storage of food, they may develop into smaller, denser, flattened or roundish, uncolored bodies, whose work is usually to gather starch into

Fig. i.— A cell (the meajaspore) from a lily ovule, filled with granular protoplasm, in which is embedded a large spherical nucleus, containing a nucleolus, and accompanied by two centrospheres, a. The line around the protoplasm represents the cell-wall, with those of the adjacent cells connected.

Magnified 500 diam. — After Guignard.

grains (fig. 3). In other cells, particularly in highly colored parts, the plastids may become of most diverse form and

size, and take on a red or yellow

color (fig. 4).

7. Wall. — The cell-wall is

Fig. 2. — A cell from the interior of the leaf of the oat, showing its wall, and some inclusions of the protoplasm. 2, the nucleus ; c , chloroplasts ; o, an oil-drop. Magnified about 1000 diam. — After Zimmermann.

Fig. 3. — Part of the cell contents of an inner cell of white potato, z, nucleus ; s, starch grains, each having been formed by a leucoplast, /, which is still attached to one side of the grain ; £, crystalloid. Magnified about 1000 diam.— After Zimmermann.

formed by the protoplasm. In green plants when first formed it consists chiefly of cellulose, with which, as it grows older, various other substances may be mixed. Some of these b c

Fig. 4. — A, chromoplasts from flower leaves of an orchid ; B, from the root of carrot ; C, from the fruit of mountain-ash. Embedded in the protoplasmic body of the chromoplast are sometimes proteid crystalloids, />, pigment-crystals, f, or starch-grains, s. Magnified about 1000 diam — After Schimper.

are present even in the young wall, and may increase with age ; others are characteristic of special changes which the wall may undergo.

IN TROD UCriON. |>

8. Growth of the cell-wall. — As the cells become older the wall may increase in thickness. It must also increase in area as the cells grow in size. The growth in area is usually accomplished by putting new particles between the older ones. Growth in thickness is rarely uniform. Pits or pores are formed in the wall when it thickens except at these spots. When the thin parts are large and only certain spots or lines grow thicker, the wall shows projecting spikes, bands, or threads.

Chapter II. Single-celled Plants And Colonies

In the lakes and pools, in ditches and slow streams, on the surface of damp rocks and wood, may be found many sorts of microscopic plants, whose entire body is merely a single cell.

9. Fission-algae. — The simplest forms of the single-celled green water plants are the fission -algae. In the central part of the cell is the nucleus, and the whole of the protoplasm is colored by the yellowish-green dye, chlorophyll. Along with it, there is a blue coloring matter, so that in mass these algae look bluish-green or even blackish. For this reason they are called blue-green algae to distinguish them from those in which only the yellow-green color is present.

10. Gelatinous colonies. — The cell-wall may be thin, but commonly it is composed of several layers, of which the outer are changed into mucilage.

This swells into a transparent jelly when wet, either becoming alike throughout or showing distinct layers. When a number of such forms grow in company (fig. 5), this jelly-like material blends into a single mass in which the associated plants seem to be embedded.

Fig

- A blue-green alga {GIa?oca/>s<i). Single individuals, A, and colonies (B-E) of various ages.

Magnified 300 diam. — After Sachs.

SINGLE-CELLED PLANTS AND COLONIES.

11. Gelatinous filament-colonies. — In other cases, instead of being held together only by the weak jelly-like portion of the cell-wall, the plants, still practically independent the one of the other, remain connected by the firmer portions of the wall into rows, forming irregularly coiled or serpentine filaments, which are embedded in a profuse jelly (fig. 6). The

Fig. 6. — Nostoc. A, a gelatinous colony, irregularly lobed. Natural size. />, a portion of a serpentine filament with five heterocysts (one at each end by which it was separated from the rest of the cells composing the filament, and three intermediate ones) and the jelly belonging to it. Magnified about 400 diam. — After Thuret and Janczewski.

real independence of the cells, even though they remain connected, is shown by the fact that such a chain may be broken up into any number of pieces and each piece will retain all its powers. Here and there in the chain there occur cells unlike the rest, whose purpose seems to be to break the chain into pieces, which work their way out of the jelly and grow into independent colonies. The association of considerable numbers of these plants in colonies gives rise to masses of jelly which vary from the size of a pin -head to 2-5 centimeters in diameter. They may be found adhering to water-weeds as clear- or dirty-green masses, or sometimes floating free (A, fig. 6).

EXERCISE I.

Nostoc or Kivularia. — I. Observe the size and form of the colonies and the consistence of the jelly enclosing them. (|n.)

OUTLINES OF PLANT LIFE.

2. Crush a bit of a Nostoc colony or a whole one of Rivularia between two glass slips, remove the upper slip, cover with water and observe the coiled (Nostoc) or radiating straight filaments (Rivularia) embedded in the jelly. (Fig. 6.)

12. Filaments of loose organization. — Of very near kin

to these plants are the oscillarias, which have received this name from the pendulum-like swinging of their tips (fig. 7). In them the cell-walls remain connected more extensively and more firmly, so that each cell is disk-shaped, and the filament is much less easily separated into its parts.

Moreover less of the wall has become jelly-like, so that often this part is not apparent and is difficult to see even when the plants are looked at with the microscope. Even though invisible, it may

Fig. 7. r-Oscillaria. a, the r ° ' J

tip; b, a portion of the be detected by the slippery feel of the

middle of a filament. Magnified 540 diam. — After plants when rubbed gently between the

Strasburger.

fingers.

EXERCISE II.

Oscillaria. 1. Observe the color of a bit of Oscillaria. (^[ 9.)

2. With needles tease out the specimen in a drop of water on a glass slip; observe the delicate thread-like form. (Fig. 7.)

3. Transfer a bit of living Oscillaria to a small glass dish or white individual butter plate with a little water; protect it from drying up with a cover; 24 hours later observe the position of the filaments. (^[ 12.)

4. Demonstration. Dip a considerable mass of Oscillaria in hot water for a moment and put in a white butter plate with as small a quantity of water as will cover it. As the water evaporates observe the color deposited on the dish at the edge of the water. (^[ 9.)

13. Feeding habits. — The feeding habits of the oscillarias are worth notice. These plants are found in permanent puddles and ditches where organic matter is decaying. The sig-

SINGLE-CELLED PLANTS AND COLONIES. 9

nificance of this is that some of the ancestors of the green oscillarias probably had offspring which, instead of living upon food prepared by means of the green coloring matter (^[ 185 ff.), learned to use the organic matter in the water, at first perhaps no more than the present oscillarias do ; but gradually they came to live exclusively upon it. As a consequence, they lost their green color and became incapable of existing where organic food cannot be had.

Bacteria.

14. Fission-fungi. — Along with the loss of color and change of habit went a diminution in size. They have now become so different that they are known as fission-fungi, and popularly as bacteria, bacilli, microbes, germs, etc. These plants, probably the descendants of common ancestors with the fission-algae, are the smallest known living things (figs. 8, 9). The diameter of many sorts does not exceed .0005 of a millimeter. That would allow 1 75 to lie side by side upon the edge of the paper on which this book is printed. Though so minute these plants have the same sort of protoplasm and cell -wall as larger ones. They increase in number rapidly by each cell dividing into two, which separate readily into independent plants.

15. Gelatin. — In the fission-fungi, as in the fission-algae, considerable masses of jelly-like material are produced, in which the plants may lie embedded. The films, sometimes smooth, sometimes wrinkled, which appear on an infusion of organic matter, such as tea or broth, are formed by masses of bacteria which rise to the surface and become embedded in the gelatinous material they produce (3, fig. 8).

Demonstration. — Steep a cupful of chopped hay in hot water for fifteen minutes, and set the infusion, loosely covered, in a warm place. After a day or two, show the film of bacteria which covers the surface of the liquid.

OUTLINES OF PLANT LIFE.

16. Cilia. — Most species are furnished with organs of movement consisting of fine threads of protoplasm protruded

Fig. 8. — Various bacteria, a, Micrococcus, the " blood-portent " ; b, zooglcea form of the same; c, Bacterium aceti, the ferment of vinegar; d, Sarcina, a harmless parasite of the human intestine, a, b, magnified 300 diam.; c, 2000 diam.; d, 800 diam.— After Kerner.

r

Fig. 9.— Bacteria stained to show cilia. A, cilia tufted at one end; B, cilia irregularly distributed over body ; C, cilium single at one or both ends. B, the bacillus of typhoid fever; C, the bacillus of Asiatic cholera. Magnified 775 diam. — After Migula.

through the wall. These, by their sudden contraction on one side, lash about like whips, and propel the cell by jerky, darting motions through the fluid in which it swims, These

SINGLE-CELLED PLANTS AND COLONIES. II

lashes, called cilia, may be single at the ends of the cell (C, fig. 9), or many at ends or sides (A, fig. 9), or the whole cell may be covered with them like hairs (B, fig. 9). They may be withdrawn or drop off when the plant comes to rest, as when they form the scums previously mentioned.

These plants are most interesting on account of their relation to health and disease, decay, fermentation, etc., which cannot be discussed here.*

17. Yellow-green algae. — Among the single-celled green plants, one of the most common groups is that represented by fig. 10, which shows one of a large series, in which the body consists of a single cell with its wall, protoplasm, nucleus, and a few relatively large chloroplasts. In this greater specialization of the protoplasm, these plants show the only advance upon the blue-green algae. The wall in such as this Pleurococcus is almost uniform and quite thin. The cells of some kinds are frequently associated in colonies, embedded in jelly or not.

EXERCISE III.

Pleurococcus. — I. Examine with a lens pieces of bark bearing Pleurococcus and similar algse. Note the irregular distribution of the green granular heaps of plants. Is there any similarity to the distribution of higher plants over uncultivated areas ?

2. After soaking a piece of bark for a few minutes, scrape off with the nail or a dull knife blade some of the green material, spread it as well as possible in a drop of water on a slip of glass, cover it with a piece of thin glass, avoiding air-bubbles, and examine with a lens. Observe the minuteness of some of the specks, which are mostly single plants The larger ones are clusters of plants.

3. Dejnonstration. Show a slide under microscope and have pupils

* For further information on these plants, see Frankland : Our Secret Friends and Foes ; Prudden : Story of the Bacteria, Dust and its Dangers. Drinking-water and Ice Supplies ; Russell: Dairy Bacteriology; Frankel (tr. by Linsley): Bacteriology (medical).

OUl^LINES OF PLANT LIFE, observe the form and color of single plants, many consisting of two or more cells still joined together, resulting from cell division. (^"17, fig. 10.)

Fig. 10. — Pleurococcus viridis. A , a single individual ; B, a colony shortly after division ; C, the same after separation. Magnified 540 diam. — After Strasburger.

FlG. 11. — Various diatoms, a, Synedra ; b, Pleurosigma ; c, d, Grammatofihora, side and top views ; e, colony of Govifihonema, with branched stalks attached to an alga ; f, g, single cells of same, more magnified, top and side views; /z, colony of Diatoma, the cells connected into a zigzag band ; /, k, colony and individuals (top and side views) of Fragillaria ; I, w, n, Coccovema. In m the pair is surrounded by jelly preliminary to the escape of the protoplasm and the formation of two new cells (auxospores) which has been completed in n.— After Kerner.

18. Shelled plants. — Other one-celled plants constitute a group known as diatoms, found in both fresh and salt waters, either attached or free-swimming (figs. 11, 12). The dia-

S1XGLE-CELLED PLANTS AND COLONIES.

toms are very various in form, and present two different aspects. When seen from the side they are generally elongated-rectangular. When looked at from above they are short-cylindric, disk-shaped, boat-shaped, or variously curved or angular. They are peculiar in having the cell-wall so filled with silica that scarcely any other material is left. Indeed the plants may be heated to a red heat and boiled in acid without destroying the form and markings of the cell-wall, so completely has it become silicified. To permit growth this rigid cell- wall is constructed in two pieces which fit together like the two parts of a pill-box (fig. 12). Each

Fig. t2.— A single diatom (Navicula amphirhynchus). A, top view; B, side view, showing overlapping of the valves. The parts shaded by lines are the chloroplasts ; the dotted part the protoplasm, with nucleus about the center of cell. Magnified 750 diam. — After Pfitzer.

of these pieces, or valves, is sculptured into regular patterns in lines and dots, which are often so excessively minute or close together as to be barely visible with the highest powers of the microscope (b, fig. 11). Seen in mass, as they may often be on the sides of a glass aquarium, living diatoms appear yellowish-brown. The chloroplasts, which are sometimes single and always few, have a brownish color in addition to the green chlorophyll.

It is not uncommon for the diatoms to form colonies by the adhesion of several or many individuals by means of gelatinous cell-walls. These colonies are ribbon-like, or zig-

OUTLINES OF PLANT LIFE.

zag chains, or even branched filaments {h, i, fig. n). Other sorts may be attached singly or in clusters by a gelatinous stalk (e, fig. n). In all cases the jelly, like the rest of the cell-wall, is a product of the protoplasm. The slowgliding movements of some free diatoms are due to the protrusion of strands of protoplasm through slits in the valves.

Fig. 13. — Various desmids. a, Micrasterias ; b, Cosmarium ; c, Xanthidium ; d, Ciosterium ; e, Staurastrum ; f, Aptogonum. Magnified about 200 diam. — After Kerner.

19. The desmids. — These form another group of one-celled green algae. They have neither the brownish color nor siliceous wall characteristic of diatoms, but are bright green cells of remarkably diverse and often beautiful forms. As a rule the cell is flattened and is divided almost into two by a deep constriction near the middle (a, b, c, e, fig. 13). Often the body of the cell is covered with warts or spine-like

SINGLE-CELLED PLANTS AND COLONIES. 1$

projections (&, c, fig. 13), or is prolonged into horn-like or hair-like lobes. These plants also frequently cohere into colonies {/, fig. 13). In that case tooth-like projections of the cell-wall may interlock.

20. Summary. — The simplest plants consist of a single cell, which is often protected by a copious mucilage. By this means also the plants are often associated in colonies of various forms. Among the green plants some possess in addition a blue coloring matter ; others a brown. Many can move about from place to place. The bacteria are degenerate relatives of the blue-green algae which have lost their green color, and thus their power to make their own food.

Chapter III. Filamentous Alg^e

Obviously some of the plants mentioned in the last chapter, such as the oscillarias, are colonies of cells well on the

way to complete union into coherent filaments whose elements are attached to each other by considerable areas of the cell-wall.

In order clearly to understand this condition, we must consider the mode of origin of the individual cells composing the row.

21. Fission. — Under conditions mostly unknown to us, in the course of its growth a cell may divide by a process known as fission. The material of the nucleus passes through a complex series of changes and separates into two parts.

In a plane between these daughter-nuclei particles are deposited to form a cell-wall (A, fig. 14). In this way a single one-celled plant of Plenro-

Fig. 14. — A, one of the final stages in cell-division. The daughter-nuclei are still connected by filaments, and across the equatorial plane particles of new cell-wall material are formed Z>, the completion of cell - division ; the daughter-nuclei have rounded off and the new wall is like the lateral walls. Magnified 880 diam.

— After Strasburger.

Fig. 15 — Diagrams of cell-division spherical cells, a, b, by the wall 1

A, division of a spherical cell into two hemi-

B, the same after further division in planes 2, 2, 3, parallel to 1. a has divided by wall 2 into a' and another cell which has again divided by wall 3 into a", a", b has divided into b' , b\ the inner of which has elongated preparatory to a division into b" , b" , as by wall 3. C, fig. A, after a second division, by wall 2, at right angles to 1.

FILAMENTOUS ALGyE.

coccus [A, fig. io) may divide into tAvo, so that it consists of two hemispherical cells, each capable of independent growth (fig. 23, A).

In the filamentous algoe the cells formed by such divisions remain connected throughout their whole extent, and as the successive divisions are parallel a cell row results (£, fig. 15).

When the divisions are in two planes the cells form a flat sheet (c, fig. 15); and when in three planes, a mass.

22. Filamentous algae.

— There is a large number of plants in which the vegetative body throughout life has the form of a filament.

The green plants of this sort live almost entirely in water or in wet places, and may be conveniently designated as filamentous algce.

23. Pond scums. — Among these none are more beautiful or interesting than the pond scums, represented in our waters by several genera (Spiro* gyra, Zygnema, Mougeotia and some others *) . They

* To the same group also belong the single-celled desmids already described.

Fig. 16. — A cell from filament of Spirogyra. ch, chloroplast (there are three in this cell) ; /, pyrenoids ; k, nucleus. Magnified 200 diam. — After Strasburger.

Fig 17. — Two cells from filament of Zygnema, showing the gelatinous sheath greatly swollen, and stellate chloroplasts, in which is a pyrenoid, with the nucleus in a strand of protoplasm between them. Magnified 245 diam.— After Klebs.

Fig. 18.— A cell from filament of Mougeotia. The darker body nearly filling cell is the chloroplast (face view) in which are pyrenoids, /, and tannin vesicles, g. If seen from a direction at right angles it would appear as a narrow stripe in the center of the cell, z, the nucleus. Magnified about 200 diam. — After Zimmermann.

may be readily recognized, during their vegetative period, by their unbranched filaments, bright green color, and slippery " feel " between the fingers.*

Under the microscope, they are at once distinguished from other filamentous algae by the shape of their chloroplasts. In Spirogyra these form one or more flattish, spirally wound ribbons, notched on the edges, and embedded in the protoplasm near the cell-wall (ch, fig. 16). In Zygnema there are generally two irregularly star-shaped chloroplasts (fig. 17) ; while in Mougeotia a single flat, plate-like chloroplast, nearly as wide as the cell, traverses its center (fig. 18). See also fig. 19.

Embedded in the chloroplasts of these and other algae are usually seen one or more angular, colorless bodies, often surrounded by a jacket of starch. These are stores of reserve food, known as pyrenoids (J>, figs. 16, 18).

In these plants there is little or no difference between the parts of the filaments. If broken into two, each part may continue growing with no damage to any part except the cells which were ruptured in severing the plant.

EXERCISE IV.

Spirogyra. — If fresh material is available examine a few filaments in a white dish for color. If preserved material is used, stain red by immersing for a few minutes in eosin (cheap red ink will answer).

Examine with a lens. Observe

1. Length ; whether broken or whole ; whether with or without branches.

2. The delicate partitions, like white lines, crossing the green (or red) filaments, dividing the protoplasm of one cell from another. Can the form of the chloroplasts be seen ? (Cf. fig. 16.) This can be readily seen only in the larger species. (][ 23.)

3. Demonstration. Mount a few fresh filaments in water. Show under moderate power the form of the chloroplasts ; the reserve food nodules ; the nucleus. (Fig. 16.)

* This slipperiness is due to the gelatinous outer part of the cell-wall (fig. 26), which is only visible after special treatment or on examining the filaments in a thin mechanical solution of Chinese ink.

FILA MEN TO US. A L GAZ.

24. Base and apex. — But other filamentous algae show a distinction between base and apex. In Ulothrix (fig. 19) the basal cell is elongated and pointed, and is colorless, because it is not furnished with chloroplasts like the others. By this pointed cell the plant is loosely attached, at least when young, to the substratum, while the green portion waves freely in the water. Thus arises a distinction into two parts, viz., the rhizoid and the thallus.

In Cladophora, Vaucheria, and their allies, the plants are generally attached by a well-developed rhizoid region, which is often branched (w, fig. 20), as is also the thallus. In contrast with the preceding, therefore, localization of growth, producing branching, may be observed.

25. Branching. — A branch begins by the growth in area of a limited portion of the cell-wall. Since growing cells are usually stretched by the water they absorb, the pressure upon the enlarged region causes the wall to bulge outward there. The convexity gradually increases as the region grows, until the swelling becomes an outgrowth whose further lengthening constitutes a branch similar to the main filament. Growth in length may be limited to the tip of a filament, or to a narrow zone including one or more cells, or it may occur indifferently in any cell, or in all cells.

Fig. 19. — Ulothrix zonata.

A young filament with rhizoid cell, r, at base. Magnified 482 diam. — After Dodel-Port.

EXERCISE V.

Cladophora. — If fresh material is at hand observe in a white dish preserved specimens are used stain for a few minutes in eosin. 1. How is the plant attached ?

OUTLINES OF PLANT LIFE.

2. Observe form and particularly the abundant branching. Can a single main axis be traced ? How many branches arise at one point ?

Fig. 20. — A young plant of Vaucheria, developing from the spore. A, mature spore ; B, the same after germination has begun ; C, plant further developed from spore, sp, with growing apex, s, and rhizoid, iu, by which it attaches itself to the mud. The chloroplasts are numerous and close together next the wall on all sides. Magnified 28 diam.— After Sachs.

26. Partition walls unnecessary. — Many algae, while externally like others, which are divided into true cells, have not the units of structure separated by cell-walls. In Vaucheria, for example, the whole of the vegetative body forms a single chamber, in which lies the undivided protoplasm, corresponding to many cells, as shown by the numerous nuclei which are distributed through it. The external walls of the cells are formed, but the partition walls are not formed.

27. External segmentation. — A plant body of this construction may attain considerable size and complexity, as in Caulerpa (fig. 21),* even to mimicking, upon a small scale, the form of leafy plants. In such cases the external walls become considerably thickened, and across the chamber, from one side to the other, run irregular bars of similar material which act as braces to prevent the collapse of the outer walls (fig. 22).

In Caulerpa, particularly, a high degree of development as to external form is reached (fig. 21). There is a stem-like