502 



plankton production (1.75 and 8.26 cm." per m.^). The produc- 

 tivity of the lake full of submerged vegetation, is, it seems, less 

 than that of one free from it, whether measured in cubic centi- 

 meters of plankton or returns for marketable fish. 



The data here presented concerning the mimical effect of 

 submerged non-rooted vegetation upon the plankton suggest 

 an interesting subject for field or laboratory experiment. In- 

 deed, experimental proof is desirable for the generalization 

 here advanced. How far it will find support in the examina- 

 tion of other localities remains to be seen, for no investigation 

 bearing upon the question seems to have been made elsewhere. 

 It should be noted that it is not maintained that all vegetation 

 is inimical to the development of the plankton, but only such 

 as successfully competes with the phytoplankton for the availa- 

 ble plant food, and thus brings by its decay no additional 

 sources for plant nutrition into the water. These conditions 

 are approximately realized where the submerged non-rooted 

 type of vegetation prevails. Where, however, by reason of the 

 local conditions or the nature of the constituent plants, the 

 aquatic vegetation adds by its decay to the fertility of the 

 water owing to its utilization of sources of food in the soil 

 and the air not available to the phytoplankton, we may expect 

 to find the development of the plankton fostered by such vege- 

 tation. These conditions are realized wherever rooted, and 

 especially emergent, vegetation prevails and contributes by its 

 decay to the enrichment of the water. A belt of littoral vege- 

 tation of this sort may thus be of considerable effect in main- 

 taining the plankton in a body of water. 



INTERNAL FACTORS AND PLANKTON PRODUCTION. 



Under this head attention will be called to certain phases 

 of plankton production with which in the present state of our 

 knowledge no environmental factors stand in apparent corre- 

 lation. From this point of view, which lays emphasis upon the 

 reacting organism rather than upon the stimulating environ- 

 ment, most of the relations and adaptations of the plankton to 



