(See page 156.)

Chapter III. (See page 156.) The lowest organisms, as the slime molds, do not have an enclosing membrane but consist of a naked mass of protoplasm. With this exception plants have an outer wall or membrane. They may consist of a single cell, as in the Bacteria, or a chain of cells, as in the filamentous Alga, or a mass of cells, as in the majority of plants, and are accordingly designated as unicellular or multicellular. The cell wall is composed for the most part of cellulose, but may be modified in various ways. Nomenclature.—The names for describing plants have been derived for the most part from studies of the higher plants, they having exclusively attracted the attention of botanists at first. GROUPS OF PLANTS. 3 But with the light which has been thrown on the relationship of the higher and lower groups of plants by the more recent study of the lower forms the older terminology has been somewhat modified. Thus, for example, we speak of the root and shoot, with its leaves, as the vegetative organs of the higher plants, and in describing the corresponding organs (where they exist) in the lower plants, we either apply these terms directly, or indi- rectly by saying that the latter are root-like, stem-like, etc. On the other hand, we now speak of the sexual organs of the higher plants as antheridia and odgonia (or archegonia) instead of classifying them roughly as stamens and pistils, the latter names being retained but with a different signification. Factors Influencing Growth.—Plants have certain inherent or inherited tendencies or characters which make up the inner constitution, and this can not be modified by external agencies except within more or less narrow limits. Depending upon this character we find plants as different in kind as the apple tree and pine growing under precisely the same conditions. In other words, the character of the structure is determined in the main by the nature of the organism. It is true that an apple tree may grow better in one locality than another, but it is still an apple tree whether it be dwarfed or attain to the full measure of its growth. These slight changes in the character are known as accidental variations. Frequently they are the result of tempo- tary conditions and are not repeated in the succeeding genera- tion. On the other hand, if the special conditions remain these individual variations may be repeated in generation after gen- eration and finally become permanent characters. The gradual change in the structure and nature of organisms which takes place through long periods of time is spoken of as EVOLUTION. In some cases specific changes in the characters of plants arise rather suddenly without any known cause and such changes are spoken of as saltations or MUTATIONS. The factors essential for growth in all cases are food, water and a certain temperature. Among the food elements we may mention as of chief importance, carbon, hydrogen, oxygen and nitrogen. Some of the other elements are also essential to most plants although they occur in relatively small proportion in the 4 BOTANY AND PHARMACOGNOSY. plant, as potassium, magnesium, phosphorus, sulphur, iron and calcium. The latter element does not seem to be necessary to the normal development of some of the Fungi and certain Alge. Water permeates all parts of the plant and when the cells are in the normal turgescent state it contains more than half its weight of water. When the supply of water falls below the normal the plants begin to droop and finally die. The need of plants varies greatly in this particular; some are aquatic in their habits and live wholly in the water; others can live only on the land; and still others are adapted to desert regions. The degree of temperature necessary for growth varies within certain limits for each kind of plant, but as is stated by Pfeffer, the greatest extremes are shown by Fungi, Bacteria and the lower Alge. Génerally speaking the most favorable temperature for growth is between 24° and 34° C. Besides the factors enumerated there are other factors which influence growth. They include light (p. 106), gravity (p. 94). mechanical agencies, etc., and are sometimes spoken of as external stimuli. It is difficult to separate those factors which act solely as exter- nal stimuli from those which are essential to the normal growth of the plant and which may be considered as physiological fac- tors. For example, light under certain conditions may be regarded as in the nature of an external stimulus and not essen- tial to the growth of the plant, while in other cases it has a direct influence on normal growth and is essential to the life of the plant, as in all plants or parts of plants where photosynthesis (p. 109) takes place. In addition to the essential food elements, there are many substances which affect the growth of plants which may be grouped as chemical stimuli, such as (a) the substances secreted by gall-forming insects, (b) in a certajn measure some of the substances produced by Fungi, (c) and numerous substances not found as normal constituents of the plant. Depending upon the amount of the substance present and the conditions under which it is supplied, the substance may act as a poison and injure the plant, or it may accelerate growth, or cause abnormal develop- ments. GROUPS OF PLANTS. 5 This subject has an important bearing on the physiological testing of drugs. Kobert statés that in determining the qualities of a new chemical, preliminary experiments should be conducted on lower plants and animals before trying it on man. Of the plants which have been used in the testing of poisons the follow- ing may be mentioned: Oscillaria, Spirulina, Nostoc, Zygnema, Spirogyra, Saccharomyces, Mucor, Elodea, Lemna, Pistia, Potamogeton, Myriophyllum, Ceratophyllum, Tradescantia, seed- lings of grasses, lupine, bean, pea, corn, etc. Plant Organs.—Depending upon the fact that the plant requires nourishment for its growth and development and that it has also to carry on the work of reproduction or propagation, —i.e., the production of new plants,—we distinguish between vegetative or nutritive organs and propagative or reproductive organs. The vegetative organs, such as the root, stem and leaves in higher plants, manufacture the food necessary for the life of the plant, while certain other more or less specialized organs or cells carry on the work of reproduction. In the lower plants, however, the whole structure is much simpler, and in some instances a cell which performs the work of a nutritive cell at one stage may become a reproductive cell at another, or, as in the case of the unicellular Algz, all the various functions of the plant may be carried on by a single cell. Generally speaking, there are two principal ways in which plants are multiplied or reproduced: (1) By CELL piviston or cell fission, and (2) by the formation of special cells known as spores. In cell division (Fig. 94) the nucleus and cytoplasm of a cell divide to form two new cells or protoplasts, which become distinct by the formation of a wall or cell-plate between the two halves. All growth in plants is dependent upon this method, and in growing parts the cells are said to be in a state of division. Owing to the plasticity of the plant organism, detached portions will often grow and give rise to new plants, as in the case of cut- tings. Growth here as in the parent plant is accompanied by cell division. In some of the lower Algz (Fig. 6) cell division is the only method of propagation, and as only the ordinary vegetative or nutritive cells of the plant are involved in the process it is some- times spoken of as vegetative multiplication. 6 BOTANY AND PHARMACOGNOSY. In both lower and higher plants, with the exceptions just noted, reproduction is also carried on by means of spores. Depending upon their origin two classes of spores are distin- guished, namely, (a) asexual spores, and (b) sexual spores. In the production of asexual spores the contents of a certain cell Oey aban ane pea od eine (F { Fro. 5. Ulothriz sonata. A, young filament with rhizoid cell (r); B, piece of filament showing escape of swarm spores; C, a swarm spore or zodspore with 4 cilia; D, biciliate gametes escaping from a filament; E, F, G, showing different stages of union of two gametes; H, young zygote or zygospore in which the cilia have been absorbed; J, 1-celled plant developed from zygote; K, young plant organizing zodspores.—After Dodel-Port. \s called a mother cell or sPoRANGIUM break up into a number of new cells sometimes called daughter cells, which escape through the cell wall. In the lower plants, particularly those growing in water or in moist places, these cells are provided with short GROUPS OF PLANTS. 7 thread-like appendages known as cilia, which enable them to move about in the water. They are known as zoOspores or swarm spores (Fig. 5, B, C), and each individual zodspore is able to produce a new plant. The number of zodspores formed in a sporangium is usually 2 to 8, as in Ulothrix, but the number may be larger. The method of cell formation which gives rise to zodspores is sometimes spoken of as INTERNAL DIVISION from the fact that they arise within the old cell and retain no relation to the old wall as is the case, in cell fission. The zodspores are at: first naked protoplasts, but later, on coming to rest, may form a wall. Sexual spores, on the other hand, are formed by the union of two cells known as GAMETES. When the gametes are similar the resulting spore is known as a zyGoSPoRE or zygote (Fig. 5, E, F, G). When the gametes are unlike, the spore produced by their union is known as an odspore. In the latter case one of the gametes is larger than the other, is less active, and is spoken of as the female gamete, odsphere, or egg (Figs. 11, 12). The other more active cell is known as the male gamete, antherozoid or sperm (Fig. 34, III). The cell giving rise to the odsphere is known as the odgonium (Figs. 8, 11, 12), while the one in which the anthero- zoid or sperm originates is called the antheridium (Figs. 8, 11, 12, 34). PLANT GROUPS. Probably the most conspicuous feature of the plant world to the casual observer is the great number and diversity of forms. It was formerly the custom to devote attention chiefly to the more prominent groups of plants, or those that produce seeds, but more recently the results of the studies on the less prominent groups, as ferns, mosses, etc., have modified our views and made it imperative that the botanist have a general knowledge at least of all the great groups of plants. The most general classification of plants is that which divides them into three great groups,—namely, (1) Thallophytes (Thal- lophyta), (2) Archegoniates (Archegoniate), and (3) Spermo- phytes (Spermophyta). 8 BOTANY AND PHARMACOGNOSY. THALLOPHYTES. The Thallophytes include the lowest orders of plants,— i.e., those simplest in form and structure. They are supposed also to represent more or less primitive types. In these plants the plant body does not show a differentiation into root, stem and leaf, as in the higher plants, and is termed a THALLUS. The thallus may branch in various ways, but the structure remains more or less uniform throughout. It should be understood, how- ever, that even in this group of plants certain cells or groups of cells may become specialized, i.c., set apart for a particular func- tion, as, for example, the reproductive cells. The Thallophytes vary in size and general appearance from minute unicellular organisms and those which are filamentous and delicately branched to large leaf-like organisms many feet in length (Figs. 6, 9. 13). The Thallophytes are divided into the two groups of plants known as (1) Alga and (2) Fungi. The Alge produce chloro- plasts, and hence are capable of manufacturing food from the inorganic substances air and water (see page 108), which fact constitutes a fundamental difference between them and the Fungi. ALG, Algz are also characterized by their habit of living in water or in moist places, and they are sometimes classified as “ fresh water alge ” and “ salt water alge” (Fig. 9). In the first group are included the common pond-scums and certain forms living on trees, moist rocks, fences and elsewhere, and in the second group the sea-weeds. In addition to the chlorophyll (see page 159) of the chloro- plasts other color substances are found in Algz, which mask the green color to a considerable extent. On the basis of their color Algz are subdivided into (1) Blue-green Alge or Cyanophycez, (2) Green Alge or Chlorophycer, (3) Brown Alge or Phzo- phycez, and (4) Red Algz or Rhodophycez. While no attempt will be made to consider these groups in detail, it should be stated that they not only vary in color, but they also vary greatly in structure and general appearance. A few type forms will be considered in order to illustrate their habits of life, GROUPS OF PLANTS. 9 Pleurococcus.—One of the commonest of the Green Alge as well as one of the simplest is Pleurococcus (Pleurococcus vulgaris) (Fig. 6). It occurs as a green coating, in both winter and summer on the moist bark of trees, moist ground, and stone walls, and is a component of some lichens. The plant is one-celled, more or less spherical, and at one stage contains a number of chlorophyll grains which finally unite to form a single plate which lies against the wall and is known as a CHROMATO- pore. Besides it contains a considerable amount of oil. An allied species (Pleurococcus viridis) contains the sugar erythrite. The plant usually reproduces by simple division, that is, one cell or plant divides to form two. The division may continue by the production of another cross wall, so that four cells result. Under favorable conditions, division may take place by the formation @s oe) Fic. 6, Plenrococcus vulgaris, Different stages of division of the cell.—After Wille of still another wall at right angles to the other two. In this way two, four and finally eight individuals arise which adhere more or less to one another, thus forming colonies. The number of individuals in a colony depénds upon the number of indi- viduals in the colony when division begins and the extent to which division is carried. Thus if there were four cells in a colony to begin with and division took place in three planes, there would be thirty-two cells in the colony at the end of the period. Spirogyra—Another one of the common Green Alge is Spirogyra (Fig. 7), one of the pond-scums, which forms float- ing green masses on ponds and shallow water in the spring. The plant-body consists of a chain of cylindrical cells forming long threads or filaments. The transverse walls are sometimes pecu- liarly thickened. The chromatophores occur in one or more spiral bands (Fig. 7, 7), which extend from one end of the cell to the 10 BOTANY AND PHARMACOGNOSY. other. In these bands are embedded protein bodies known as pyrenoids. The nucleus lies in the center of the cell and is con- nected with the cytoplasmic layer lining the walls of the cell by delicate threads of cytoplasm. Spirogyra may be propagated vegetatively by one or more cells of a filament breaking off and forming new individuals by cell division. The plant is also reproduced by means of zygo- Fic. 7. Il. Spirogyra stictica, showing parts of two filaments with band-like chroma- tophores (chloroplasts), in which are embedded spherical pyrenoids. Nuclei are shown in some of the cells with delicate threads of cytoplasm radiating from them. Two of the cells (a,a,) of the adjoining filaments (A, B) are beginning conjugation. I, S. Heeriana, showing different stages of conjugation. In the upper cells, the contents have rounded off previous to the rupture of the adjoining walls of the two filaments. The two middle cells show the contents passing from one cell into the opposite cell. In the lower cell to the right the zygospore is shown.—After De Bary. spores, as follows: The cells of two adjoining filaments each send out processes (Fig. 7, /J, a, a), which meet; the end walls are absorbed, forming a tube through which the contents from one cell pass over irito the other (Fig. 7, /); the contents of the two cells then fuse, after which the mass becomes surrounded by a cellulose wall. The spore thus formed may remain dormant over winter, and the following spring germinate and form a new Spyro- gyra filament or plant. This method of reproduction is known GROUPS OF PLANTS. Ir as CONJUGATION, and the zygospore is called a resting spore. It should be explained that certain cells, as well as spores, may lie dormant for a period, as during the winter season or at other times, when the conditions are unfavorable to growth, and then renew their activities, these being known as “ resting cells.” Vaucheria (Fig. 8) is another common green alga which may also be selected as showing the habits of this group of plants. The plant has a branching thallus and lives in shallow Fic. 8. Vaucheria sessilis. A, sporangium from which the multiciliate zodspore is escaping: B, resting zodspore; C, D, germinating zoospores with growing point (s); E, plant showing root-like organ of attachment (w), spore from which the plant is develop- ing (sp), F, showing in addition two odgonia (og) and an antheridium (h).—After Sachs. water or on moist earth, being attached to the substratum by means of delicate root-like processes sometimes spoken of as thizoids (Fig. 8, «). In the thin layer of protoplasm lying near the wall are numerous nuclei and small oval chromatophores. Numerous oil globules are also found in the protoplasm, and cal- cium oxalate crystals may occur in the cell-sap. Vaucheria furnishes an example of a plant whose interior is not segmented by cell walls. In other words, the cavity within the outer or enclosing membrane is continuous, and such a plant 12 BOTANY AND PHARMACOGNOSY. is said to be coenocytic, i.¢., like a syphon. But it should be borne in mind that the plant contains a great many nuclei, and as we have seen (page 2) a nucleus with its associated cytoplasm constitutes a unit of work. Hence such a plant as Vaucheria is in a certain sense equivalent to a plant having as many uninucleate cells as it has nuclei. It would probably be better to call such a plant multinucleate rather than unicellular. Reproduction by means of asexual spores is brought about as follows (Fig. 8, 4): A cross wall is formed near the end of one of the branches, the end portion constituting a sporangium. The contents, including numerous nuclei group themselves into one large zodspore, which escapes through an opening in the sporan- gial wall, and after swimming about for a time comes to rest and germinates, giving rise to a new plant (Fig. 8,C, D). This large zodspore is multinucleate and multiciliate, there being two cilia for each nucleus, and by some botanists is considered to be an aggregation of numerous biciliate zodspores. It is also of interest to note that the zodspores of Vaucheria appear to arise by a‘grouping of the cytoplasm and the nuclei already existing in the sporangium rather than by repeated divisions of a single nucleus. Another method of reproduction in Vaucheria (Fig. 8. F) is that by means of odspores, or spores formed by the union of egg and sperm cells. Two special branches are formed on the thallus as short side shoots. One of these branches, known as the odgonium (Fig. 8, og), is somewhat egg-shaped and sepa- rated from the thallus by means of a cross wall. It contains a great many chromatophores and considerable oil, and has a com- paratively thick wall. The apex is somewhat beaked and con- tains colorless protoplasm. The second branch, which is known as an antheridium (Fig. 8, 1). is smaller, somewhat cylindrical and curved towards the odgonium. It is also cut off from the thallus by means of a cross wall. The antheridium contains very little chlorophyll, but a great many sperm cells. These are oval or egg-shaped