DISCUSSION OF RESULTS. 51 



affect plants. A comparison of the temperature curves of the 

 two years shows that the summer maximum came somewhat 

 earlier in 1899 than in 1900. This might explain the earlier 

 maxima of the Crustacea, but I do not quite undestand why 

 the plants should not have been equally affected. 



COMPARISON OF CURVES OF TOTAL PLANKTON" WITH CURVES OF 

 PLANKTON CONSTITUENTS. 



As has already been noted, the curves of plant production 

 follow very closely the curves of total plankton, for it is to plants 

 that the great differences in the amount of plankton are due. 

 There are some marked exceptions to this general rule, like the 

 great maxima of certain of the diatoms. 



In general terms it may be said that the curves for animals 

 also follow the total plankton curves, most of them reaching 

 their maxima in the summer months. There are many excep- 

 tions, however. Some of the Crustacea are perennial in their 

 occurrence, and some have winter maxima. Somte of the roti- 

 fera, too, occur only in the winter mjonths. Generally speak- 

 ing, it is in the deep lakes that we find more of those animals 

 having winter maxima, although there are some exceptions. 

 Some of the Lake Winnebago rotifera, for instance, are found 

 only in the winter season. It is evident, however, that the 

 greater uniformity of conditions in the deep lakes would make 

 winter production more possible. 



HORIZONTAL DISTRIBUTION. 



One of the questions to which especial attention was paid 

 was the matter of the uniformity of horizontal distribution. I 

 discussed this question in some detail in a former paper 

 (Marsh J 97, pp. 218-223) expressing my own belief that the 

 numbers of Crustacea might vary widely in different parts of 

 a lake, and that they might, at some times, be aggregated to- 



