Relation of Inorganic to Organic Bodies 53 



green algae. Its importance as a field of study appears when 

 we remember that it is amongst these, rather than amongst 

 the nucleate green plants, that definite and invariable response 

 to environal stimuli first became a permanent phenomenon 

 and hereditary condition of each species. 



Ecologically the group is of exceptional interest, and merits 

 much investigation in the near future. As to temperature 

 range about forty of the species {13: 253) might appropriately 

 be called "hot spring Algse" or "thermophilic Algae." Thus 

 while Brewer overestimated in giving 94.5° C. as the tempera- 

 ture of the water in which some grew, Setchell (37), Tilden, 

 and others have carefully shown that it runs up to 75° or 76° C. 

 in the Western American geyser regions. At least half of the 

 above number of species are found habitually and normally 

 in siliceous and carbonated hot springs, at temperatures of 

 45-65° C. As Cohn, Weed, and others have proved, they not 

 only form an "abundant vegetation in gelatinous (colloid) 

 silica and carbonate of lime, they precipitate these by chemical 

 action and deposit extensive tracts of these minerals." 



As already pointed out (p. 27) it is extremely probable that 

 extensive rock masses, which greatly resemble these sinter 

 and travertine minerals, and which are met with in all the 

 great rock formations back to the archsean period, had their 

 origin in like manner. It seems, therefore, justifiable to con- 

 clude that if forty or more living species of Protophycese, now 

 left to us, can thrive and multiply abundantly at temperatures 

 from 50° to 75° C, many primitive protoplasmic structures or 

 species must have had an equally high resisting capacity, and 

 may even have formed a temporarily })redominant type of 

 vegetation, over extensive thermic areas of the world. 



Equally true is it that at least some resist low tem])eratures 

 well. For while Kiitzing states that the cold waters of high 

 mountains are not suited for their growth, it is true that in 

 situations where they are often exposed during ^x-inter to at 

 least — 10° C, as on rock faces and amongst boulders of hill 

 regions in the United States and in Switzerland examined by 

 the writer, they still multiply and persist. 



