489 



It is different, however, in the matter of nitrites, which are 

 about twice as abundant in Thompson's Lake as in Quiver, and 

 the same ratio also holds approximately for the free and al- 

 buminoid ammonia. These are all substances indicating or- 

 ganic matters in the process of decay, or available for decay 

 and thus for plant nutrition. These data show clearly that in 

 these particulars the waters of Thompson's Lake are much 

 richer than those of Quiver, and this difference is undoubtedly 

 one of the factors on which the contrast in plankton produc- 

 tion depends. The more abundant plankton of the former 

 lake may itself be one of the sources contributing to the or- 

 ganic decay here indicated. 



This contrast in the chemical constituents in part at least 

 follows from the sources from which the waters in the two 

 lakes are derived. River water impounded from receding 

 floods and more or less charged with sewage and industrial 

 wastes constitutes the principal source of the water in Thomp- 

 son's Lake. Spring and creek waters replace this very 

 slowly, and every rise in the river introduces a new supply 

 of richly fertilized water which at levels above six feet trav- 

 erses the whole lake. Quiver Lake is subject to like invasions, 

 but its more abundant supply of creek and spring water coun- 

 teracts their influence to some extent and soon replaces their 

 contributions. 



A consideration of these other factors, current and chem- 

 ical constituents, makes it probable that they also are efficient 

 in causing the contrast in plankton productivity in the two 

 lakes. How much of this contrast is due to vegetation and 

 how much to their agency is a matter upon which conclusive 

 evidence is needed. Experiment in the field may yield con- 

 clusions that will be final. 



Some evidence corroborative of my contention that the 

 vegetation of Quiver Lake is inimical to the development of 

 its plankton is afforded from two sources; (1) the examination 

 of Matanzas Lake, and (2) the comparison of the plankton pro- 

 duction of Quiver Lake in years of abundant and scant vegetation. 



