By HELEN C. DE S. ABBOTT.
The succession of plants from the lower to the higher forms will be reviewed superficially, and chemical compounds noted where they appear.
When the germinating spores of the fungi, myxomycetes, rupture their walls and become masses of naked protoplasm, they are known as plasmodia. The plasmodium aethalium septicum occurs in moist places, on heaps of tan or decaying barks. It is a soft, gelatinous mass of yellowish color, sometimes measuring several inches in length.
The plasmodium2 has been chemically analyzed, though not in a state of absolute purity. The table of Reinke and Rodewold gives an idea of its proximate constitution.
Many of the constituents given are always present in the living cells of higher plants. It cannot be too emphatically stated that where "biotic" force is manifested, these colloidal or albuminous compounds are found.
The simplest form of plant life is an undifferentiated individual, all of its functions being performed indifferently by all parts of its protoplasm.
The chemical basis of plasmodium is almost entirely composed of complex albuminous substances, and correlated with this structureless body are other compounds derived from them. Aside from the chemical substances which are always present in living matter, and are essential properties of protoplasm, we find no other compounds. In the higher organisms, where these functions are not performed indifferently, specialization of tissues is accompanied by many other kinds of bodies.
The algae are a stage higher in the evolutionary scale than the undifferentiated noncellular plasmodium. The simple Alga protococcus3 may be regarded as a simple cell. All higher plants are masses of cells, varying in form, function, and chemical composition.
A typical living cell may be described as composed of a cell wall and contents. The cell wall is a firm, elastic membrane closed on all sides, and consists mainly of cellulose, water, and inorganic constituents. The contents consist of a semi-fluid colloidal substance, lying in contact with the inner surface of the membrane, and, like it, closed on all sides. This always is composed of albuminous substances. In the higher plants, at least, a nucleus occurs embedded in it; a watery liquid holding salts and saccharine substances in solution fills the space called the vacuole, inclosed by the protoplasm.
These simple plants may be seen as actively moving cells or as non-motile cells. The former consist of a minute mass of protoplasm, granular and mostly colored green, but clear and colorless at the more pointed end, and where it is prolonged into two delicate filaments called cilia. After moving actively for a time they come to rest, acquire a spherical form, and invest themselves with a firm membrane of cellulose. This firm, outer membrane of the Protococcus accompanies a higher differentiation of tissue and localization of function than is found in the plasmodium.
Haeatococcus and plasmodium come under the classes algae and fungi of the Thallothyta group. The division4 of this group into two classes is based upon the presence of chlorophyl in algae and its absence in fungi. Gelatinous starch is found in the algae; the fungi contain a starchy substance called glycogen, which also occurs in the liver and muscles of animals. Structureless bodies, as aethalium, contain no true sugar. Stratified starch5 first appears in the phanerogams. Alkaloids have been found in fungi, and owe their presence doubtless to the richness of these plants in nitrogenous bodies.
In addition to the green coloring matter in algae are found other coloring matters.6 The nature7 of these coloring matters is usually the same through whole families, which also resemble each other in their modes of reproduction.
In form, the algae differ greatly from filaments or masses of cells; they live in the water and cover damp surfaces of rocks and wood. In these they are remarkable for their ramifications and colors and grow to a gigantic size.
The physiological functions of algae and fungi depend upon their chemical differences.
These facts have been offered, simple as they are, as striking examples of chemical and structural opposition.
The fungi include very simple organisms, as well as others of tolerably high development, of most varied form, from the simple bacillus and yeast to the truffle, lichens, and mushrooms.
The cell membrane of this class contains no pure cellulose, but a modification called fungus cellulose. The membrane also contains an amyloid substance, amylomycin.8 Many of the chemical constituents found in the entire class are given in Die Pflanzenstoffe.9
Under the Schizomycetes to which the Micrococcus and Bacterium10 belong are found minute organisms differing much in form and in the coloring11 matters they produce, as that causing the red color of mouldy bread.
The class of lichens12 contains a number of different coloring substances, whose chemical composition has been examined. These substances are found separately in individuals differing in form. In the Polyporus13 an acid has been found peculiar to it, as in many plants special compounds are found. In the agariceae the different kinds of vellum distinguish between species, and the color of the conidia is also of differential importance. In all cases of distinct characteristic habits of reproduction and form, one or more different chemical compounds is found.
In the next group of the musiceae, or mosses, is an absence of some chemical compounds that were characteristic of the classes just described. Many of the albuminous substances are present. Starch14 is found often in large quantities, and also oily fats, which are contained in the oil bodies of the liverworts; wax,15 organic acids, including aconitic acid, and tannin, which is found for the first time at this evolutionary stage of the plant kingdom.