52 Prof. B. Moore, Messrs. E. Whitley, and T. A. Webster. 



process of evolution. The details of seasonal variation in growth resulting 

 from intensity of illumination will be given in a subsequent paper ; here will 

 be considered the changes in the algae and the sea water due to the action of 

 Kght apart from seasonal variations. 



There is in the case of marine plants none of that uncertainty which 

 obtains in the case of the higher terrestrial plants as to how much of the 

 nitrogen being built into organic compounds comes from the roots. Even in 

 the case of such massive plants as Laminaria and Fucus it is obvious that the 

 roots are merely modes of attachment to the rocks, and that the whole plant 

 is built up from the sea water. It is an impossibility that nitrogen could be 

 extracted from the hard stones to which the plants are anchored, and in the 

 case of the floating diatoms, and other minute green cells, which form the 

 phyto-plankton, floating free in the sea, it is clear that the whole organism is 

 formed from the sea water. Hence the entire plant life of the sea is produced 

 by the action of sunlight upon the water of the sea and its dissolved 

 constituents. In so far as sources of ready formed and easily absorbable nitro- 

 genous compounds are concerned, the sea water is remarkably poor, and the 

 volumes of sea water necessary to feed the algae with nitrogen, were this the 

 source, would be immense. Thus, Gebbing* found the amount of nitrogen as 

 ammonia present in sea water to be only 0*05 mgrm. per litre, and the amount 

 as nitrite plus nitrate as 0"47 mgrm. per litre.f These results are confirmed 

 by some to be given later in this paper. 



This paucity of nitrogenous compounds in sea water, while it indicates that 

 the nitrogen of the plant tissues is probably derived from the dissolved 

 elemental nitrogen of the atmosphere, is not however clear proof, for the sea 

 water, for example, contains but a trace of that silica from which the 

 skeletons of the diatoms are derived. It might be argued that in the restless 

 movement of the sea the volume of water which daily laved the plants was 

 ample to compensate for the small amount of dissolved nitrogenous compounds 

 in the water. To settle this query it is obviously necessary to grow marine 

 algae in a limited volume of sea water and then to determine the amount of 

 nitrogen fixed. If this latter many times exceeds the amounts of nitrogen 

 present as ammonia, nitrites, and nitrates in the sea water used, then clearly, 

 for here there is no soil to obscure the issue, this fixed nitrogen must come 

 from the dissolved nitrogen in the sea water, which in turn came from the 

 nitrogen in the air. 



* J. Gebbing, ' Centralb. f. Bacteriol., 2. Abth.,' vol. 31. 



t Gf. also Moore, Edie, Whitley, and Dakin, "The Nutrition and Metaboliani of 

 Marine Animals," ' Biochem. Journ.,' vol. 6, p. 255 (1912) ; Eaben, ' Wissensch. 

 Meeresuntersuch., Kiel,' vol. 8 (1905). 



