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 favorabie to the quantita- 
tive development of the plankton as were the conditions prey- 
alent in summer and autumn. 
As a whole, then, temperature changes ‘bane 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 alge 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 
