Tuffen West, del. Edmund Evans.
Bacteria, as I have said, were for a long time classed with fungi under the name of Schizomycetes. But the more recent researches into their organisation, and more especially into their mode of reproduction, show that they rather more resemble a group of algæ devoid of chlorophyll. Zopf asserts that the same species of algals may at one time be presented in the form of a plant living freely in water, or in damp ground, in association with chlorophyllaceous protoplasm, and at another in the form of a bacterium devoid of green colouring matter, and receiving nourishment from organic substances previously elaborated by plants or animals, thus accommodating itself, according to circumstances, to two very different modes of existence.
That widely-distributed single-cell plant, the Palmoglœa macrococca of Kützing, that spreads itself as a green slime over damp stones, walls, and other bodies, affords an example. If a small portion be scraped off and placed on a slip of glass, and examined with a half or a quarter-inch power, it will be seen to consist of a number of ovoid cells, having a transparent structureless envelope, nearly filled by granular matter of a greenish colour. At certain periods this mass divides into two parts, and ultimately the cell becomes two. Sometimes the cells are united end to end, just as we see them united in the actively-growing yeast plant; but in this case the growth is accelerated, apparently, by cold and damp. Another plant belonging to the same species, the Protococcus pluvialis, is found in every pool of water, the spores of which must be always floating in the air, since they appear after every shower of rain.
Protococcus pluvialis is furnished with motile organs—two or more vibratile flagella passing through perforations in the cell-wall—whereby, at certain stages, they move rapidly about. The flagella are distinctly seen on the application of the smallest drop of iodine. The more remarkable of the several forms presented by the plant is that of naked spores, termed by Flotow Hæmatococcus porphyrocephalus. These minute bodies are usually seen to consist of green, red, and colourless granules in equal proportions, and occupying different portions of the cell. They seem to have some share in the after subdivision of the cell ([Fig. 283]). There are also still-cells, which sub-divide into two, while the motile cells divide into four or eight. It is not quite clear what becomes of the motile zoospores, B, but as they have been seen to become encysted, they doubtless have a special function, or become still-cells under certain circumstances.
It appears that both longitudinal and transverse division of the primordial cell takes place; and that the vibratile flagella of the parent cell retain to the last their function and their motion after the primordial cell has become detached and transformed into an independent secondary cell ([Fig. 283], G).
Fig. 283.—Cell Development. (Protococcus pluvialis.)
Protococcus pluvialis, Kützing. Hæmatococcus pluvialis, Flotow. Chlamidococcus versatilis, A. Braun. Chlamidococcus pluvialis, Flotow and Braun.