GERMAN PLANKTON INVESTIGATIONS. 329 



A study of the results already obtained by the German 

 investigators leads to the following conclusions. In 

 general the shallower waters are richer in plankton than 

 the deeper seas, and of the latter the Sargasso Sea is 

 exceptionally poor. In the shallower seas the influence of 

 the bottom and of the solid land is quite appreciable. 

 The plants have therefore in a smaller layer of water more 

 food material, whereas in the deeper seas the inorganic 

 nitrogen-containing food material is distributed over a 

 very much larger volume of water, only the upper layers 

 of which are capable of supporting plant life. The food 

 material in the lower layers, which are devoid of sunlight, 

 cannot be used up by plants. Apstein (5) divided the 

 fresh water lakes of Holstein into two groups, i.e., rich in 

 plankton and poor in plankton. Brandt investigated the 

 proportion of nitrates in the different lakes by means of 

 the diphenylamine-sulphuric acid reaction (9, p. 228, 

 footnote). The investigation of the lakes rich in plankton 

 gave a result which showed them to be rich in nitrogen 

 compounds ; while the lakes poor in plankton were found 

 on the contrary to contain but a small proportion of these 

 compounds. 



Another important result deduced from the quantitative 

 plankton investigations is that the tropical and 

 sub-tropical seas are comparatively poor in plankton, 

 while the arctic seas are richer. On the dry land the 

 contrary is the case with regard to the vegetable products. 

 It would appear that the true cause of the wealth of the 

 cold and the poverty of the warm seas in plankton is to be 

 sought for in the different amount in which the denitrify- 

 ing bacteria are present, and the influence which they 

 exert on the presence of the nitrogen compounds in the 

 wafer. If, as is apparently the case, a not inconsiderable 

 denitrihcation takes place in the ocean, then it is probable 



