ORIGIN AND EVOLUTION OF LIFE 303
which distinguishes the proteins of the bacteria : nitrogen is also a large constituent of animal proteins.
Percentage or Elements in the Proteins^^
Carbon 50.0 - 55.0
Hydrogen 6.9 - 7.3
Oxygen 19.0 - 24.0
Nitrogen 18.0 - 19.0
Sulphur 0.3 - 2.4
Closest to the bacteria in structure are the so-called "blue-green algae" or Cyanophyceae, found everywhere 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 bine-green algae which in this case are red. Unlike the true algae the cell nucleus of the Cyanophyceae ordinarily is not sharply limited by a membrane, and there is no evidence of distinct chlorophyll-bodies, although chlorophyll is present. Their only method of reproduction is that known as vegetative multiplication, in which an ordinary working cell (individual) divides to form two new individuals. 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 among the various lower organisms concerned in earth-building, the algae rank first, the foram- inifera second, and the corals third. In a forthcoming work by F. W. Clarke and W. C. Wheeler they remark upon these earth-building activi- ties as follows :
The calcareous algsB are fo 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 ca^es they far outrank the corals in importance, and of late years much attention has been paid to them. On the atoll of Funafuti, fdr example, the algae Lithothamnium and Halimeda rank first and second in importance, followed by the foraminif- era, 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 Algonkian time,^® together with calcareous
3* Moore, F. J., 1915, p. 199. Xucleic proteins contain a notable amount of phosphorus as well.
35 Coulter, John Merle, 1910, pp. 10-14. seWalcott, Charles D., 1914.
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