296 THE CIRCULATION OF NITROGEN [PART III 



these ideas, and by means of them accounts not only for the 

 greater luxuriance of plant life in the cold seas, but also for the 

 occurrence of the well-known maximum of plant production in 

 the sea during the spring months. 



There is still another explanation of the anomalous distribution 

 of plant life in the warm and cold seas. The reader will remember 

 that Putter^ shewed that both animal and plant metabolism is 

 much more intense in warm than in cold sea water. With in- 

 creasing temperature the rapidity of respiration of a cold-blooded 

 animal also increases, and it uses up more oxygen, and gives off 

 more carbon dioxide. With increasing intensity of respiration there 

 is an increase in the general metabolism of the organism, so that 

 the same animal uses a greater mass of food-stuffs per hour when 

 the water is warm than when it is cold. Therefore in the warmer 

 seas the ordinary food-requirements of animals and plants are 

 greater than in the cold seas. 



We must distinguish between what Putter calls the " Betriebs- 

 stoffwechsel," and " Baustoflfwechsel " of an animal or plant. The 

 former we may call the ordinary current metabolism of its body, 

 the assimilation of food-material and excretion of waste products 

 which must necessarily proceed if the organism is to continue to 

 live. The latter is the structural metabolism, the setting aside of 

 assimilated food-substance for the formation of new tissue material, 

 of eggs, buds, generally of new individuals. The former is the 

 anabolism and katabolism of the ordinary life-processes of the 

 stationary organism ; the latter is the anabolism of the growing 

 plant or animal, or of the animal which is actively reproducing. 

 It is the metabolism of growth and reproduction. 



Now in warm and cold seas alike the reproductive phase has 

 become a habit of all organisms, recurring at regular intervals of 

 time, which are determined by physical conditions. Alike in warm 

 and cold seas there is a population of animals and plants which is 

 exactly adjusted to the amount of food-materials present. If the 

 cun^ent metabolism of a cold-blooded animal or marine plant 

 increases with the temperature it follows that a lesser mass of 

 food-stuffs will suffice for the same population in a cold sea than in 

 a warmer one. But if the organisms of the plankton of a warm 



^ Stoffhaushalt cles Meeres. 



