236 THE CONDITIONS OF LIFE IN THE SEA [PART III 



stuffs, nitrogen compounds, phosphoric acid, or silica, is present 

 in the sea in minimum proportion, and so rules the production. 

 It is possible to ascertain the ratios in which the elements, 

 nitrogen, phosphorus, and silicon, exist in the tissues of the more 

 abundant plankton organisms, and Brandt^ did so by making 

 chemical estimations of the composition of catches which consisted 

 predominantly of certain organisms, such as copepods, peridinians, 

 and diatoms. It should be possible, from a consideration of the 

 results of such analyses, to ascertain in what proportions these 

 different organisms require the three elements, for the demand 

 for each will be proportional to the amount of each element 

 present in the tissues of the organism (when due account 

 is taken of the different absorption coefficients of the salts 

 containing the elements). Now from such analyses Brandt" 

 came to the conclusion that it was the nitrogen which was present 

 in minimum proportion, but since it was the older estimations of 

 the proportions of silica and phosphoric acid in sea water that he 

 considered, it is probable that his conclusion must be revised. 

 Thus the dry substance of diatoms contains about 1'8 ^q of nitrogen, 

 and about 54*5 *^/q of SiOa shewing that about thirty times as much 

 silica as nitrogen is required by these organisms. Yet the greatest 

 amount of the latter substance found in the sea by Raben was 

 only 1*4 mgrms. per litre, while nitrogen was present to the extent 

 of about 0'2 mgrm. per litre. Thus silica was only about seven 

 times as abundant in the sea as nitrogen, though thirty times as 

 much was required. Therefore the silica was present in minimum 

 proportion and not the nitrogen. 



So far as the diatoms are concerned it would appear that it is 

 the proportion of silica in the sea water that determines the 

 production. Raben's results are so instructive in this connection 

 that I have represented them in the diagram on p. 237, along with 

 the curve of seasonal variation of diatoms in Kiel Bay. It will 

 be noticed that the plankton curve relates to the year 1892, while 

 the silica curve is for the period 1902 — 4. But a consideration 

 of the Kiel plankton investigations shews that the form of the 



1 Chemiifche Zusamin. Pkmktons. 



- In " Stoffwechsel im Meeres," 2n(i Abhandlung, Wiss. Meeresunt. Kiel Komm. 

 Bd. VI. Abth. Kiel, 1902. 



