202 SCIENCE PROGRESS 



amounts of the various foodstuffs required by the plants (and 

 the equivocal organisms with a plant-like mode of nutrition) are 

 in the same ratio as the amounts of those substances which are 

 contained in their dry substance. Now Brandt showed from 

 his analyses of plankton catches that diatoms contain, on the 

 average, about i"8 per cent, of nitrogen in their dry substance, 

 and peridinians (the next commonest organisms in the sea which 

 feed like plants) about 2'o8 per cent, of nitrogen, also in their 

 dry substance. 1 But Knop 2 gives only 0*3 per cent, of phos- 

 phoric acid in the dry substance of marine algae, and this is 

 probably not far from the amount which is also contained in the 

 diatoms and peridinians. Therefore these organisms require 

 more nitrogen than phosphorus, but there was apparently more 

 of the latter element in the sea in an easily assimilable form. 

 The obvious conclusion is, that the calcium phosphate in the 

 sea is not the substance which governs the production. 



But Raben's later and more exact determinations of the amount 

 of phosphoric acid in the waters of the Baltic compelled a 

 reconsideration of this view. It has been clearly shown, by the 

 quantitative plankton investigations of the Kiel biologists, that 

 there are very well-marked periods of maximum propagation 

 of the various protozoa and protophyta of the plankton. Thus 

 diatoms are certainly at a maximum during March and April, 

 and peridinians are at a maximum in the autumn. Now it is in 

 the latter season that the phosphoric acid is at a maximum of 

 abundance in solution in the sea. Remembering that according 

 to the results of Raben the amount of this substance in the sea 

 is less than was formerly supposed, we see that it is possible 

 that the phosphoric acid may accumulate during the early part 

 of the year, and that, when it has attained its maximum, then 

 the peridinians begin to multiply in increased numbers, so as 

 to cause them to assume their predominance in the autumn 

 plankton. 



So also with the silica, only the seasonal fluctuation of this 

 foodstuff is more clearly indicated by the analyses ; and so also 

 the seasonal fluctuation of the diatoms is more clearly shown by 

 the results of the quantitative plankton catches than any other 

 group of organisms in the sea — a result which is to be expected 



1 Brandt, " Beitrage zur Kenntniss d. chemischen Zusammensetzung d. Plank- 

 ton," Wiss. Meeresunt. Kiel. Komm. Bd. 3, 1898. 



2 Knop, Kreislauf des Stoffes. 



