40 PHOTOSYNTHESIS 



more food than an equal area of land. East ^^ considers that most of the 

 plants, which are as much the primary source of food of sea animals as 

 of land animals, are found in waters not over 200 feet in depth, and that 

 such areas of the sea would approximately equal 5 per cent of the land 

 area of the globe. With the possible exception of certain rather restricted 

 regions as in the North Sea and Baltic, where the economic importance of 

 sea life has long been recognized, few careful surveys have been made of 

 the production of the sea. In most cases the products of photosynthesis 

 in the sea are harvested indirectly. That is, while some algae are used 

 as a source of food in China and Japan, this is not very general and man 

 confines himself largely to the consumption of animals which feed upon 

 sea vegetation or other sea animals. In many cases this is several steps 

 removed from the original plant source. The result is a tremendous waste 

 of energy, so that man finally obtains an exceedingly small quantity of 

 food from a very large amount of carbon dioxide reduced by the marine 

 plants. The diatoms and holophytic peridines are the great marine con- 

 verters of solar energy. Upon these and other sea plants we depend for 

 our sea food ; the very intricate relationships between the various forms 

 of marine life make the determination of the "food producing value" of 

 an area of water an exceedingly complex problem. 



The chemistry of the sea and its relation to the gases of the atmosphere 

 has been the subject of much experimental and theoretical study. ^" While 

 at first these problems appeared to be relatively simple, when studied more 

 minutely, particularly in relation to the activities of living organisms, many 

 complex conditions became apparent. The solubility of the gases of the 

 atmosphere, the influence of the salinity of the ocean and of temperature 

 on this and similar conditions determine the fitness of the ocean for plant 

 and animal life. While most of the constituents of the ocean are main- 

 tained in relatively constant proportions the concentration of carbon 

 dioxide and to a lesser degree also oxygen are found to undergo consider- 

 able variation. These variations together with the intimately associated 

 hydrogen ion concentration of the sea are of paramount importance to 

 living organisms. 



Schulz ^' has made a very careful study of the aeration of the North 

 Sea and Baltic Sea and his recent results are here given to illustrate the 

 conditions existing for life in the sea. For more detailed information the 

 literature cited must be consulted. Table 3, taken from Schulz's publica- 

 tion shows the percentages of the different gases of the atmosphere in 

 natural waters. 



'° East, Mankind at the Crossroads, p. 71. 



''Murray, J., and Hjort, J., The Depths of the Ocean. London, 1912. For- 

 chammer, Phil. Trans. Roy. Soc, 155, 203-262 (1865). Dittmar, Challenger Report, 

 Physics and Chemistry, vol. 1, 1-251 (1884). Quinton, R., L'eau de Mer. Paris 

 (1904). Clarke, Data of Geochemistry, Bull. U. S. Geol. Survey No. 770 (1924). 

 Stieglitz, Carnegie Inst, of Washington Pub. 107 (1909). Schulz, Arch, deutsch 

 Seezvarte, 40, 1 (1922), 41, 1 (1923). 



"Schulz, B., Die Naturmissenschaften, 12, 105-113, 126-133 (1924). 



