495 



emergent vegetation, principally Scirpus, which, on account of 

 its growth and structure, does not reach an advanced stage of 

 decay until ice and winter floods have broken" it down. With 

 rising spring temperature it yields to decay and releases a great 

 store of nitrogen which the phytoplankton can utilize. Both 

 of these types of vegetation are rooted in the humus and allu- 

 vial deposits of the lake, and both are to some degree emergent. 

 They thus draw their supply of food (dissolved salts and gases) 

 largely from soil waters and the air, and less from the supiDly 

 in solution in the water of the lake. The submerged and non- 

 rooting vegetation {CeratophyJhi}}) and Elodea) is not abundant 

 in Flag Lake, so that the food supply in the lake waters is not 

 drawn upon to any great extent by the aquatic vegetation, and 

 it thus becomes available for the phytoplankton, which, in 

 turn, supports the zooplankton. The products of decay of the 

 succulent and emergent vegetation, on the other hand, are in 

 large part released directly into the lake waters, and at times 

 (fall and spring) when the plankton reaches its greatest devel- 

 opment in this region. Owing to its character and to the pro- 

 tected situation of the lake the vegetation is never swept away 

 by floods, nor is the lake traversed by any marked current as 

 are both Thompson's and Quiver lakes. The fertilizing effect 

 of the decaying vegetation is thus more localized in this region 

 than in the other bodies of water examined by us. 



The data from Flag Lake thus throw light upon the effect 

 of emergent and rooted vegetation — which is typically of the 

 littoral type — upon the plankton. They indicate that this kind 

 of vegetation favors the development of the plankton by add- 

 ing to the food materials in the water, while at the same time 

 it does not to a large degree compete with the phytoplankton 

 in the consumption of the food thus released by its decay. 



In 1896 a series of examinations of the local distribution 

 of the plankton in Quiver, Matanzas, and Thompson's lakes was 

 made by the pumping method, and since the collections were 

 made in the areas of vegetation as well as in the open water 

 they might also be examined to determine, if possible, the effect 



