Elements of Structural and Systematic Botany | Page 7

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.
CLASS II.--Schizophytes.
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 (Cyanophyce?) 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.
[Illustration: FIG.?6.--Blue-green slime (Oscillaria). A, mass of filaments of the natural size. B, single filament, ��?300. C, a piece of a filament that has become separated. s, sheath, ��?300.]
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