Evolution of Plants 327 



inhabitants of the warmest waters of thermal springs as con- 

 forming to such conditions? Much can be said in favor of the 

 latter view. Thus so far as surely determined the cell of a 

 sulphur, of an iron, or of a silicate bacterium consists only 

 of a cell-wall that would correspond much in aspect and rela- 

 tion to the colloidly precipitated membrane of a Traube cell, 

 and of a finely granular or at times vacuolated foam-like proto- 

 plasm within. In living examples the granules seem at times 

 to be particles of food, at times as in sulphur bacteria pure 

 sulphur masses. Some however, by staining and by chemical 

 tests, seem to show chromatin granules that may represent 

 evolving nuclear substance, as yet in diffuse state. 



But the sulphur or Thiobacteria, when living amid free 

 hydrogen sulphide, are able to utilize the latter for their life 

 needs. For, as Fischer (39: 67) well puts it, "seeing that a 

 solution of SHg in water is very easily decomposed by the 

 oxygen of the air, and free sulphur deposited, the sulphur 

 bacteria would be able to take advantage of this oxidation 

 for their life processes, even if they merely had the power of 

 existing in H2S solution. The HgS, entering their cells, would 

 be oxidized by absorbed atmospheric oxygen, and the sulphur 

 set free would represent an abundant source of energy for 

 further oxidation." Then "the oxidation of this sulphur 

 represents a very abundant supply of energy, a supply that 

 is probably far more than sufficient to cover the wants of the 

 organism living under the conditions already described, and 

 building up its protoplasm from the minute traces of fatty 

 acids and ammonia contained in the water it lives in." 



Autotrophic action evidently occurs also in the iron and 

 the siliceous organisms. It seems therefore highly probable 

 that these, even more perfectly than the Blue-green Algae, 

 represent the most ancient organisms now left to us. 



But the pink and purple bacteria probably are derived from 

 the colorless sulphur ones by slow elaboration of a pink pig- 

 ment in the outer cell region that is sensitive to and capable 

 of absorbing red sunlight or even infra-red or dark rays as 

 a source of energy. So "the Erythrobacteria have therefore 



