CHAPTER XXIV 



STUDIES IN CRYPTOGAMS 



The pupil who has acquired skill in the use of the com- 

 pound microscope may desire to make more extended ex- 

 cursions 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 pro- 

 toplasm 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, bacterid). 



(Fig- 1 35-) 



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 form- 

 ing an endospore which is very resistant to extremes of environ- 

 ment. No sexual reproduction is known. 



Bacteria are very widely distributed as parasites and sapro- 

 phytes 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 



182 



