PELAGIC PLANT LIFE 383 



large numbers to play a momentous part in the general economy. 

 Still careful study distinctly reveals the fact that the plants 

 of the sea are in striking disproportion to the animals. The 

 most reliable results so far obtained are those due to Lohmann's 

 researches in Kiel Bay. He studied the quantities of all the 

 plankton organisms for a whole year with great thoroughness, and 

 calculated the volume of the various groups in the plankton of the 

 different water-masses at all seasons. To us his most interesting 

 discovery is that the plants on an average made up 56 per cent 

 and the animals 44 per cent of the total plankton. In the 

 winter months the plants were easily outnumbered by the 

 animals, and from December to February they formed scarcely a 

 third of the total plankton. In the summer, on the other hand, 

 they predominated, and made up sometimes even as much as 

 three-quarters of the whole. Plants which are reproduced by 

 division must necessarily decrease rapidly whenever vigorous 

 augmentation ceases, if animals are constantly consuming 

 numbers of them. 



The life-cycle of animals, with its growth-period in youth Life-cycle of 

 and propagation in maturity, is more complicated than that of ^""^^^'^• 

 plants, and gives them a better chance of withstanding unfavour- 

 able conditions of existence. A lower temperature necessarily 

 reduces their intensity of breathing, and thus diminishes their con- 

 sumption of nourishment, and it may be also that they can go 

 without feeding for a comparatively long time, during which they 

 live upon reserve matter that they have accumulated at more 

 favourable seasons. Damas made some interesting studies of 

 the life-cycle of the larger copepods, and found that propagation 

 may require a higher temperature than what is necessary for 

 conserving vital energy, and that therefore these forms can 

 delay their propagation until the conditions of existence become 

 more favourable, so that the young animals may have the rich 

 nutriment required for their growth. Calamis finmarchims, the 

 commonest large copepod of the Norwegian Sea, abounds 

 wherever the temperature is over 2° C, in both its half-grown 

 and full-grown stages, but propagation does not begin till the 

 temperature rises to 4" C, either owing to warmer water-masses 

 arriving from the south, or to heating at the surface from the 

 atmosphere. 



Lohmann has endeavoured to calculate the relation between Relation 

 the augmentation of the algse and their consumption by animals production 

 throughout the year in Kiel Bay. He assumes that there is a and consump 

 daily accession of 2>'^ per cent to the volume of the algse, and '°" ° ^^^' 



