SEA-WATER AS A FOOD SOLUTION 99 



the above indispensable food substances. Conditions of life 

 in the sea generally are far more uniform than on land. The 

 enormous variations in moisture which land plants and animals 

 have to contend with can be left out of consideration when 

 dealing with the conditions of existence of marine organisms. 

 The soil, which plays such an important part in the growth, 

 distribution, and development of land flora, can be practically 

 left out of account in dealing with marine plants. The range 

 of temperature on land varies from 65 C. in Tibet to -66*6 C. 

 in Siberia that is, a range of 130. In the open sea, on the 

 contrary, the range is only 33'8, from -2'8 to 31 C. It is 

 highly significant that marine organisms are never exposed to 

 lower temperatures than -2'8 C., since at that temperature 

 the sea becomes covered with ice, which protects the lower 

 layers of water from a further diminution of temperature, even 

 when the temperature of the air sinks much lower. 



In spite of the remarkable uniformity of temperature in the 

 sea (when considered from a biological standpoint), there is a 

 great difference in the species of organisms met with in cold 

 and warm regions. And this difference extends to the 

 abundance in which these organisms are met with. If the 

 wealth of vegetable life in the sea were dependent only on 

 sunlight, we should expect to find the tropical seas, like the 

 tropical lands, with an abundance of vegetation. The fact 

 that the production of organic from inorganic substances takes 

 place by the aid of chlorophyll more rapidly in strong sunlight 

 and at high temperatures would lead us to expect this. But 

 the growth of plants is dependent still more on the presence 

 of the food substances in solution in sea-water. If a single one 

 of the indispensable elements be present in small quantities, 

 then the production of the vegetable plankton is scanty. All 

 marine plants depend for their nourishment on the water in 

 which they live, and not on the soil or bottom of the sea, in 

 this respect affording a marked contrast to land plants. This 

 is true not only for floating algae and diatoms, but also for 

 bottom-living algae (seaweeds) as well. The food substances 



