CHAPTER XXIV
STUDIES IN CRYPTOGAMS
The pupil who has acquired skill in the use of the compound
microscope may desire to make more extended excursions
into the cryptogamous orders. The following
plants have been chosen as examples in various groups.
Ferns are sufficiently discussed in the preceding chapter.
Bacteria
If an infusion of ordinary hay is made in water and allowed to
stand, it becomes turbid or cloudy after a few days, and a drop
under the microscope will show the presence of minute oblong
cells swimming in the water perhaps by means of numerous hair-*like
appendages, that project through the cell wall from the protoplasm
within. At the surface of the dish containing the infusion
the cells are non-motile and are united in long chains. Each
of these cells or organisms is a bacterium (plural, bacteria).
(Fig. 135.)
Bacteria are very minute organisms,—the smallest known,—consisting either of separate oblong or spherical cells, or of chains, plates, or groups of such cells, depending on the kind. They possess a membrane-like wall which, unlike the cell walls of higher plants, contains nitrogen. The presence of a nucleus has not been definitely demonstrated. Multiplication is by the fission of the vegetative cells; but under certain conditions of drought, cold, or exhaustion of the nutrient medium, the protoplasm of the ordinary cells may become invested with a thick wall, thus forming an endospore which is very resistant to extremes of environment. No sexual reproduction is known.
Bacteria are very widely distributed as parasites and saprophytes in almost all conceivable places. Decay is largely caused by bacteria, accompanied in animal tissue by the liberation of foul-smelling gases. Certain species grow in the reservoirs and pipes of water supplies, rendering the water brackish and often undrinkable. Some kinds of fermentation (the breaking down or decomposing of organic compounds, usually accompanied by the
