72 BOTANY 



and the outer part of the protoplast may contain chlorophyll, and 

 perhaps constitute an imperfect chromatophore. The young cells 

 of many Bacteria appear perfectly homogeneous, but there may 

 usually be detected granules, some of which react much like the 

 chromatin-granules of the higher plants, and very likely are homolo- 

 gous with them ; but unlike the chromatin of the higher plants, 

 these are not segregated into a definite nucleus. The view that the 

 whole protoplast of the Bacteria represents a nucleus, the cytoplasm 

 being nearly or quite wanting, is not confirmed by the latest re- 

 searches. 



Cell-wall. The cell-wall of the Schizophyta usually does not show 

 the cellulose reaction. In the Bacteria it generally contains nitro- 

 gen, while in the Schizophyceae, it is very often mucilaginous or 

 gelatinous in consistency. Where this is highly developed, the 

 plants form colonies imbedded in masses of jelly, often of great 

 size, as in Nostoc commune. This gelatinous matrix is not to be 

 looked upon simply as a modified cell-wall, but is to a great extent 

 a direct excretion from the protoplast. Similar gelatinous envelopes 

 are found in many Bacteria; and, as these are of definite form in 

 each species, it is easy to identify them, even without a microscopic 

 examination (Fig. 52). 



Distribution 



The Schizophyta occur wherever any life is possible, and are 

 adapted to extraordinarily varied conditions. Some of the Bacteria 

 can endure temperatures above the boiling point of water, while no 

 degree of cold can destroy their vitality. They can be dried up for 

 prolonged periods without suffering, and indeed can be subjected 

 to all sorts of unfavorable conditions without succumbing. Many 

 forms live within the bodies of other organisms ; some exist in the 

 depths of the ocean, while others swim upon its surface. The nitri- 

 fying Bacteria live in the soil, while myriad bacterial germs floating 

 in the air settle on every exposed object, and under favorable condi- 

 tions multiply with great rapidity. 



The extraordinary powers of resistance to heat and other condi- 

 tions fatal to most organisms, as well as the great simplicity of their 

 cell-structure, make it probable that the Schizophyta are the direct 

 descendants of forms which lived before the conditions upon the 

 earth were suitable for more highly organized forms of life. 



Classification of Schizophyta 



Two classes of the Schizophyta are usually recognized, the 

 Schizomycetes, or Bacteria, and the Schizophyceae, or Blue-green 

 Algae, also known as Cyanophyceae, or Phycochrornacege. The first 



