350 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



great increase was made after June 26 when the nitrate was .20* parts per mil- 

 lion. At both of these times, however, the nitrite was very high and no doubt 

 nitrate was being formed very rapidly by conversion of nitrites into nitrates. 

 In fact the data indicate such a process most definitely. In one case I found 

 (Station T; July 12, Fig. 8) a rapid increase of plants while both nitrates 

 and nitrites were low (Nitrate .025* and Nitrite .006 parts per million.) If 

 this last case could be considered representative it would mean that pre- 

 formed nitrate or nitrite content is not a determining factor in plant growth, 

 but one analysis, cheeked though it was, is too slender a basis for so broad 

 a statement. It does, however, serve to emphasize the probability that the 

 nitrogen supply in so far as it is a determinant acts not as a preformed, static 

 condition, but as a dynamic process whereby the complex molecules of al- 

 buminoid are converted to constantly sim])ler and higher oxidized forms 

 availa]>le for plant assimilation. 



It might be thouglit that plants al)sorb consideral)le nitrate from the 

 sediment of the bottom. Several considerations make this improliable: 



(1) Althougli no analyses of the sediment were made, it is unlikely it 

 contained a very large amount of nitrate. The analyses taken of samples 

 very near the bottom show even a lower concentration at that place. Then 

 too, diffusion would tend to remove the soluble form from the sediment. 



(2) The lower part of the stem of plants like Potamogetons and Elodea, 

 which were most abundant has very little physiological function, but serves 

 merely as a holdfast. 



(3) It is difficult to understand how a plant stem of small diameter 

 would be able to transport a highly soluble and readily dialyzed substance 

 through a space filled with water in which a low tension of the same substance 

 exists, Anthout losing it to the surrounding medium. 



(4) In these same regions of densest growth floating ])lants were especially 

 abundant (Algae and Spirodela predominating). These plants of course had 

 no direct connection with the bottom. 



After consideration of the above facts it seems very unlikely that the 

 content of the sediment has any appreciable effect upon the plant growth 

 except as ft affects the composition of the water al)Out the plants. 



Summary: The following facts are indicated liy the data: 



(1) The groAvth of plants greatly reduces the amounts of nitrates and 

 nitrites in regions where currents are inhil)ited, and to a less extent in all 

 regions of the lake. This reduction became marked in this lake al»out the 

 first of July. 



(2) The contents of all the compounds under consideration rose during 

 the winter with the exception of the nitrite which fell almost to zero. 



(3) Nitrate and nitrite rose very rapidly in the months of April and 

 JMay and first few days in June. This was no doubt due to the bacteria 

 getting started before the plants and so building up a surplus of these 

 forms. 



