320 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



of dry organic substance. The annual bill of fare of the 

 plankton animals is calculated to be 133 grams for every 

 square metre of surface water. Consequently the grand 

 total of annual production of plankton per square metre 

 of the Baltic is 150 grams, or for the whole sea 8J million 

 kilograms. According to Biebahn and Rodewald, the pro- 

 duce of one square metre of cultivated land would be 

 annually 179 grams. The fertility of the sea is thus seen 

 to be on this reckoning about 20 per cent, below that of 

 the land. But when it is taken into consideration that 

 the estimation is based on " cultivated land," and when it 

 is further considered what an enormous extent of land is 

 incapable of cultivation, it will be seen that it is by no 

 means improbable that the produce of the sea is really 

 greater than the produce of the land. It seems however 

 to be less favourable. 



Detailed results of the method of investigation accord- 

 ing to chemical analysis have been published by Brandt 

 (8), and he has further instituted a most interesting and 

 instructive comparison between the chemical constituents 

 of the plankton, or single groups of plankton animals, and 

 the land plants and edible fish and invertebrates. 



For the three principal groups of organisms of the 

 plankton Brandt gives the following results. All the 

 figures are percentages : — 



