I02 



THE ORIGIN AND EVOLUTION OF LIFE 



where in fresh and salt water and even in hot springs, as well 

 as on damp soil, rocks, and bark. The characteristic color of 



the Red Sea is due to a 



free-floating form of 

 these blue-green algae, 

 which in this case are 

 red. Unlike the true 

 algtC, the cell-nucleus of 

 the Cyanophyceae or- 

 dinarily is not sharply 

 limited by a membrane, 

 and there is no evidence 

 of distinct chlorophyll 

 bodies, although chloro- 

 phyll is present. In the 

 simpler of the unicel- 

 lular Cyanophyceae the 

 only method of repro- 

 duction is that known 

 as vegetative multipli- 



FiG. 15. Fossil and Living 

 Alg-E Compared 



C. A living algal pool colony near 



the Great Fountain Geyser, 



Yellowstone Park. After 



Walcott. 



B. Fossil calcareous algas, Crypto- 



zoon prolifcrum Hall, from 



the Cryptozoon Ledge in 



Lester Park near Saratoga 



Springs, N. Y. These algse, 



which are among the oldest 



plants of the earth, grew in cabbage-shaped heads on the bottom of the ancient 



Cambrian sea and deposited lime in their tissue. The ledge has been planed down 



by the action of a great glacier which cut the plants across, showing their concentric 



interior structure. Photographed by H. P. Gushing. 



Fossil alga;, NnvJandia conccntrica, Newlandia Jrondosa, from the Algonkian Belt 



Series of Montana. After Walcott. 



