6 PLANKTON OF WISCONSIN LAKES 



beef and to 63 per cent in the hind quarter of mutton. On a fat free 

 basis, then, the beef and mutton would yield a much larger percentage 

 of crude protein than the plankton. 



While this investigation has involved a rather large series of plank- 

 ton observations and a fairly detailed quantitative and chemical study 

 of the material that was secured, yet it can scarcely be regarded as more 

 than an introduction to this fertile field of research. Not only should 

 such studies be extended to other types of lakes for purposes of com- 

 parison, but it should also be the aim to secure data that would even- 

 tually make it possible to estimate the annual production of plankton 

 material with some degree of exactness. The first problem presents no 

 special difficulties, but the second one is very complicated. The latter 

 involves a study of the rate of reproduction and the length of life of 

 the various plankton constituents in their natural environment; such 

 studies would also include investigations relating to the effect of the 

 physical and chemical factors of the environment upon these organisms. 

 The food relations among the plankton organisms themselves are in- 

 cluded in this question, as well as those between the plankton and non- 

 plankton forms. It is necessary, also, to ascertain the average weight 

 of the different kinds of planktonts in order to determine the relative 

 values of the different forms. Numerous factors, therefore, are in- 

 volved in this problem ; some of them are physical, some chemical, and 

 some are biological in character. 



