THE LAW OF THE MINIMUM IN THE SEA 203 



when we consider the overwhelming importance of these organ- 

 isms in the metabolism of the sea. Now this association of 

 the change of abundance of the diatoms, and the change of 

 abundance of silica in the sea, is so clearly brought out by 

 Raben's analyses that I have expressed the two things in one 



diagram. 



In the following figure the thin line indicates the 



I 9 O t 



Variations in the amount of silica in the sea and in the abundance of the plankton. 



abundance of plankton in Kiel Bay in 1892. The shape of the 

 curve is the same for every year studied. It indicates the volume 

 of the catch of total plankton obtained by a quantitative net ; 



