EVOLUTION OF ALG^ 103 



cation, in which an ordinary working cell (individual) divides 

 to form two new individuals. In certain of the higher forms, 

 in which there is some differentiation of connected cells and in 

 which we seem justified in considering the " individual" to be 

 multicellular, multiplication is accomplished through the agency 

 of cells of special character known as the spores. No evidences 

 of sexual reproduction have been observed in the Cyanophyceae. 

 The sinter deposits of hot springs and geysers in Yellowstone 

 Park are attributed to the presence of Cyanophyceae.^ 



With the appearance of the true algae the earth-forming 

 powers of life become still more manifest, and few geologic 

 discoveries of recent times are more important than those 

 growing out of the recognition of algae as earth-forming agents. 

 As early as 1831 Lyell remarked their rock-forming powers. 

 It is now known that there are formations in which the algae 

 rank first among the various lower organisms concerned in 

 earth-building. In a forthcoming work by F. W. Clarke and 

 W. C. Wheeler, they remark upon these earth-building activ- 

 ities as follows: "The calcareous algae are so important as 

 reef-builders that, although they are not marine invertebrates 

 in the ordinary acceptance of the term, it seemed eminently 

 proper to include them in this investigation. In many cases 

 they far outrank the corals in importance, and of late years 

 much attention has been paid to them. On the atoll of Funa- 

 futi, for example, the algae Lithothamniiim and Halimeda rank 

 first and second in importance, followed by the foraminifera, 

 third, and the corals, fourth." 



Algae are probably responsible for the formation of the 

 very ancient limestones; those of the Grenville series at the 

 very base of the pre-Cambrian are believed to be over 60,000,- 

 000 years of age. The algal flora of the relatively recent Al- 



* Coulter, John Merle, 1910, pp. 10-14. 



