THE ALG^ 



237 



®» 



many miles in extent. It has been estimated that the 

 diatomaceous earth of the Bohemian deposits contains 

 fortj'-one million diatoms in every cubic inch. Similar 

 deposits are to-day being formed in swamps, in lake-beds, 

 and over large areas of sea-bottom. 



The conditions of life under which 

 algse can exist are extremely various. 

 One unicellular species, the red snow 

 plant, S^jhoerella nivalis, gives a pink 

 color to many square miles of snow in 

 the arctic regions. Some of the blue- 

 green algcB, on the other hand, live in 

 hot springs at a temperature of 145° 

 Fahrenheit. It is usually stated that 

 alg£e differ from fungi in being 'self- 

 supporting, but at least one parasitic 

 species is kno^Ti. 



The green algse have a special inter- 

 est for the scientific botanist from the 

 fact that they are supposed to be the 

 ancestors of the mosses. 



Few algse have much direct eco- 

 nomic value as articles of human food '^' ^p°^^*^ °* -^ emahon 



(great It magniiied) ; 



or as sources of manufactured prod- 

 ucts. Some, as the " Irish moss," the 

 dulse, and " Ceylon moss," are eaten. 

 Rockweeds are considerably used as fertilizers. Diatoma- 

 ceous earth is sold under various names for polishing silver 

 and other metals. Algse, particularly of some minute float- 

 ing marine groups, are of the greatest importance as food 

 for shellfish and for many of the small organisms which 

 form the diet of fishes. 



\. 



Fig. 108. Red Alex. 



B, portion of thallus of 

 a red alga. Lejolieia, 

 Tvith tetra.spores, t. 



