8 THE BIOLOGY OF THE SEASONS 



process of " photo-synthesis " being necessarily at a 

 standstill in the dark. 



That is a simple case, but many correlations re due to 

 a circuitous nexus, as in the case of the relatio between 

 the amount of sunshine in Spring and the abundance of 

 mackerel around our coasts. Mr. G. E. Bullen finds that 

 for the years 1903-1907 there appears to be a correlation 

 between the number of mackerel taken during May and 

 the amount of Copepod plankton, upon which the mackerel 

 feed, taken in the neighbourhood of the mackerel fishing 

 grounds during the same month. Mr. W. J. Dakin 

 shows that the food of the Copepods consists largely of 

 the vegetable organisms of the plankton, such as diatoms, 

 and of Infusorian-like organisms called Peridinidae. But 

 the production of this microscopic plankton, the " stock " 

 of the " sea-soup/' depends partly on the composition of 

 the sea-water, partly on the temperature, and partly on 

 the amount of light available. There seems to be no 

 correlation between the surface temperature and the 

 abundance of mackerel, but Dr. E. J. Allen of the Ply- 

 mouth Marine Laboratory, who has brought all these 

 facts eloquently together, has shown that there is a real 

 correspondence between the amount of sunlight and the 

 catches of mackerel. 



In some cases the correspondence between external 

 events and vital events seems unmistakable, and yet we 

 cannot understand the connection. Thus Professor Kofoid 

 has brought forward some striking evidence of a correlation 

 between lunar changes and quantitative changes of river 

 plankton, which seems even more mysterious than the 

 connection between the full moon and the excitement of 

 lunatics, or between sun-spots and trade-strikes. 



There are several correlations as certain as that between 

 the Spring sunshine and the supply of mackerel at Billings- 



