480 



months, while the amplitude of the December and January 

 pulses was surpassed but once from June to December. Con- 

 ditions under the ice at minimum temperatures were thus in 

 these years and localities quite as favorable to the quantita- 

 tive development of the plankton as were the conditions prev- 

 alent in summer and autumn. 



As a whole, then, temperature changes bear an important 

 relation to the course of plankton production, but at times they 

 are not more potent than other factors. An abundant plankton 

 may develop at any temperature within the normal seasonal 

 range provided other factors favor it, but generally the ampli- 

 tude is less in lower or in falling temperatures, and greater in 

 higher or in rising ones. 



The relations here discussed between the volume of plank- 

 ton and temperature depend primarily upon adaptations of 

 particular species to temperature — a subject which will be dis- 

 cussed in another connection. 



LIGHT AND PLANKTON PRODUCTION. 



There are at hand no adequate data on this subject, and it 

 is, moreover, complicated with the thermal and other forms of 

 solar energy and with the problem of turbidity in the water 

 itself. No detailed comparison is afforded by the data, espe- 

 cially since the more minute forms are not adequately repre- 

 sented by the catches of the silk net, and it is largely these 

 synthetic organisms, chlorophyll-bearing algae and flagellates, 

 which are most dependent upon light for their growth and re- 

 production. Our data alike of light and plankton are thus 

 deficient. Nevertheless, in the chain of relations, the catch of 

 the silk net — largely of animal plankton — is, at most, but a 

 few links removed from these synthetic organisms, and it must 

 therefore in some measure reflect their quantitative fluctua- 

 tions. Our data suggest a few inferences concerning the rela- 

 tion of light and plankton production. 



The period of greatest illumination lies between March 20 

 and September 22, and owing to the proximity of these dates 



