42 Causes and Course of Organic Evolution 



that is associated with organisms living in the warmest waters 

 (60-75° C.)j through pink and pink-purple toward brown- 

 green, blue-green, and olive-green; the last being formed in 

 waters only slightly, if at all, above maximal land-plant tem- 

 peratures (35-40° C.)- These species are all ranked as Blue- 

 green Algae, Protophycese, or Cyanophycese. Since it has 

 been shown also that the purple bacteria, like green plants, 

 set free oxygen during daylight, it may be that these are the 

 forms which yield us the stages in gradual elaboration of plant 

 chlorophyll, a purely chemical substance, but by whose activity 

 alone green plants are able to decompose carbon dioxide and 

 to so link up the carbon T\dth elements of water (HgO) as to 

 form therefrom sugar, the fundamental "organic" crystalloid, 

 that is the first step in, and the starting point for, elaboration 

 of all higher plant foods. 



According to the above view, then, we might consider all 

 green or chlorophylloid plants to have originated from primi- 

 tive colorless cells, evolved by slow degrees during the ar- 

 chsean epoch. These, like the nitrogen bacteria, may at first 

 have been colorless, and simultaneously utilized nitrogen com- 

 pounds in the process of protein elaboration, as well as nascent 

 carbon for formation of carbohydrates like sugar. By increas- 

 ingly perfected development of a pigment through yellow, 

 I)ink, purple, purple-blue, and blue-green stages a definite 

 green substance — chlorophyll — eventually became so important 

 an energizing material that the first steps in linking up of 

 inorganic into organic compounds was effected wholly through 

 its activity. So may have originated the great monophyletic 

 group that culminated in the abundant ramifications of the 

 dominant or green plant series. 



But a fourth group of primitive plants now seems to survive 

 in localities like those favored by the purple bacteria. The 

 iron bacteria of the present day form a distinct physiological 

 series, in that they obtain their supplies of energy by utiHzing 

 and oxidizing iron salts. As already stated (p. 16) the bog- 

 iron ores of nearly every stratified rock group probably had 

 their origin in connection with these iron bacteria. But it 



