206 SCIENCE PROGRESS 



results of three catches of peridinians was 3*28 per cent, of 

 nitrogen in the dry substance ; that of two mixed catches 3*16 

 per cent. ; and that of two catches which consisted chiefly of 

 diatoms was 2*11 per cent. Now the amount of water in which 

 these catches were contained could be ascertained from a know- 

 ledge of the "filtration capacity" of the net used, from the area 

 of opening of the latter, and from a measurement of the depth 

 to which it was lowered. Thus Brandt : estimated that these 

 quantities of nitrogen were contained in one cubic metre of 

 water: in the case of three catches of peridinians 0*031 grm. ; 

 in the case of the two mixed catches o'oi6 grm. ; and in the case 

 of the two catches of diatoms 1*019 grm. Generally speaking, 

 the water in the Bay of Kiel contained from 0*007 to 0*04 grm. 

 of nitrogen in a cubic metre — that is, from 0*007 to 0*04 parts 

 per million. 



These values when compared with the analyses of Natterer 

 show that if the plankton of the regions investigated by the 

 latter were as rich as that of Kiel Bay, the nitrogen would 

 certainly be in minimum quantity. Natterer did not investigate 

 the plankton, so that a direct comparison of the organic and 

 inorganic nitrogen in the seas dealt with by him is not possible. 

 But we know that the seas of the Mediterranean area are not 

 so productive as those of the north. It is, however, possible 

 to compare the results obtained for the Kiel seas. According 

 to Raben's analyses the water of the North Sea and the Baltic 

 contains, on the average, not less than 0*2 parts of inorganic 

 nitrogen per million. Now the organic nitrogen present in 

 the same sea area is not less than 0007, and not more than 

 0*04 per million. Therefore there is at least four times as 

 much inorganic as organic nitrogen in this water. Is this food- 

 stuff present in minimal proportion ? We must remember that 

 not all the compounds of nitrogen which are dissolved in the 

 sea can be assimilated by the marine plants. In the case of 

 a land plant the co-efficient of absorption by the root-hairs is 

 probably only a few per cent., but in the case of the diatoms 

 this co-efficient is certainly much higher, for these live bathed 

 in a solution of the foodstuffs and because of their extremely 

 large surface area when compared with their volume, the 

 co-efficient of absorption is high — probably not less than 

 50 per cent. It is possible that in the warmer periods of the 



1 Brandt, " Beitr. Chem. Zusamm. Planktons." 



