46 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



the relative difference is much greater in the case of the deep 

 lakes than is true of the shallow lakes. 



I have already remarked, in comparing the plankton of Green 

 lake with that of Lake Winnebago, that Green lake has the 

 greater amount of plankton in the winter, and J^ke Winnebago 

 the greater amount in the summer. I think we may say that 

 this general comparison holds in regard to all deep and shallow 

 lakes. The deep lakes because of the later date of freezing, 

 the larger amount of water, and hence the larger amount of 

 available oxygen, will have a greater amount of winter plank- 

 ton, while the shallower lakes will in summer have the greater 

 amount of plankton because of the favorable conditions for 

 plant growth produced by the higher temperature of the water 

 and the relatively large area of the bottom that is reached by 

 the sunlight. 



