44 PHOTOSYNTHESIS 



atmosphere in relation to the great chmatic alternations as evidenced by 

 glacial periods and epochs of luxuriant vegetative growth, is, after all, 

 a matter of speculation upon which we cannot enter here. These are 

 questions which involve thorough discussion from the geological view- 

 l>oint **^ and upon which there still exist divergent opinions. The condi- 

 tions of interchange of carbon dioxide between atmosphere and sea as they 

 exist at present are sufficiently complex. The biochemistry of the sea is 

 of itself a chemical constellation. 



The living organisms in the sea exert a decided influence on the 

 composition of the water. The plants absorb large quantities of carbon 

 dioxide and convert it into organic compounds. United with these are 

 hydrogen, nitrogen, sulphur and phosphorus. These compounds are in 

 turn appropriated by the animals of the sea, constituting a system fully as 

 complex as the life of land plants and animals. Many of these animals 

 liberate carbon dioxide from bicarbonates, precipitating calcium carbonate, 

 and thus enormous calcareous deposits of tufa and travertine are formed. 

 After death the bodies of both plants and animals decompose yielding 

 ammonia, hydrogen sulphide and carbon dioxide. These compounds are 

 again drawn into the metabolism of other organisms. The whole forms 

 an enormously complex series of cycles involving fine adjustments and 

 stupendous quantities of material, an evaluation of which has not yet 

 been attained. 



The whole question of the carbon dioxide-content of the atmosphere 

 in different parts of the world, under varying conditions and its relation 

 to the sea and the life therein is in need of thorough study over a longer 

 I^eriod of time. It is only within recent years that reliable methods of 

 analysis have been perfected. Such a survey should include studies not 

 only at marine stations near the coast but also at localities far distant from 

 the mainland and with consideration of the effect of the great streams. 



McClendon *' has made some very valuable contributions to the meth- 

 ods of analysis of sea-water. Some of his conclusions are here quoted. 

 "It has been supposed that the amount of CO2 in sea-water regulates the 

 growth of seaweed, but the reverse is probably more nearly correct. The 

 respiratory quotient of marine organisms seems to be about 0.7 to 1.0 and 

 the respiration of animals and plants reciprocal. Some marine bacteria 

 take their oxygen from nitrates, but this effect must be minute, since the 

 supply of nitrates is small. The atmosphere cannot be the chief regu- 

 lator of the CO2 of the sea, since there is about 30 times as much CO2 in 

 the sea as in the air. There is always a superabundance of COo in sea- 

 water to supply the needs of green, red, or brown seaweed, but by using 

 it the plants increase the pH of the water. It seems probable that the 

 plants grow rapidly until the pH that is most favorable to them is ex- 



^•Chamberlin, T. C, and Salisbury, R. D., GcoJoqv. New York, 1907. Vol. I, 

 640. Arrhenius, 5". Phil. Mag. (5), 41, 237 (1896). Abbot and Fowle, Ann. 

 Astrophxs. Obs. Smithsonian Inst., 2, 172, 175 (1908). 



"McClendon, J. F., Carnegie Inst. Wash. Pub. No. 251, p. 37 (1917). 



