PLANT LIFE 135 



the freezing point of fresh water, while very 

 closely related species in the tropics pass their 

 lives in water with a temperature of 80° F. 

 The metabolism — the rate of growth, of diges- 

 tion, and of reproduction — is greatly retarded 



;pbnu K^ v..m«i4 Sea Surface , biu« *im««i» 



f««""»i.": Ownk nmlcUn m4 IWiton Inntfnm. Ar*m^i \ 



thnUm^amiak-tmimirmui^caroinfw^ ^ 



khyvuH Plankton 

 •nd Nokton 



I 





Fia. 8. — Diagram showmg the oceanic faunal and floral areas. 



in the cold polar waters and accelerated in the 

 warm equatorial waters. In the shallow 

 waters marine organisms must accommodate 

 themselves to strong currents, to abundant 

 sunlight, to rapid changes of temperature and 

 salinity, and hold their own against many 

 varied competitors and enemies, whereas in 

 the deep sea there is no sunlight, a nearly 

 constant low temperature, and no rapid cur- 



