CHAPTER VII 



LIFE IN THE OCEAN : PLANTS 



The term biosphere is now used by naturalists 

 to designate that mantle of living matter 

 which clothes the globe wherever the atmos- 

 phere, the hydrosphere and the lithosphere 

 are in contact and intermingle. On the dry 

 land living beings do not rise very high above, 

 or penetrate very deep below, the surface, 

 but in the ocean it is different. Life is present 

 everywhere throughout the mass of ocean 

 waters, from the equator to the poles and from 

 the surface down to the bottom at a depth of 

 six English miles. 



The visible rays of the sun penetrate the 

 ocean waters down to a depth of over 3000 

 feet, but even the actinic rays do not penetrate 

 beyond 5000 feet. This superficial layer 

 affected by sunlight is called the photic zone 

 of the ocean, and throughout its whole extent 

 vegetable life is present, often in great abun- 

 dance, in the form of vast floating meadows of 

 unicellular algae. Herbivorous animals feed 

 on these minute algae and other plants, and 

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