CHAPTER XIX 



ALG.E, SEAWEED, CHLOROPHYLL CELLS, THEIR 

 ORIGIN AND USE EFFECT ON RAYS OF LIGHT 

 THE PROVIDERS OF OXYGEN ALL LIFE IM- 

 POSSIBLE WITHOUT CHLOROPHYLL LIGHT AND 

 HEAT ESSENTIAL TO ITS ACTION. 



THE Algae, when existing alone, constitute the 

 lowest and simplest forms of green or chlorophyll- 

 bearing plants. Algae are mostly aquatic, and live 

 either entirely in the water or require wet or con- 

 stantly damp positions, in which only they thrive. 

 Their spores, or certain cells that split off from 

 the others, can resist the absence of moisture, and 

 serve to perpetuate their growth when favorable 

 conditions again return. Many of them are very 

 minute. Desmidiaceae and Diatomacea3 in their 

 thousand varieties being microscopic only, whilst 

 some of the Fucacea are among the largest of all the 

 vegetative world. Macrocystis Pyrifera, off the S. 

 and S. W. coast of South America, sometimes exceed- 

 ing a thousand feet in length. The floating masses 

 238 



