348 . PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



considerable in amount. The regions near the town showed a higher nitrogen 

 content as a look at the data will show. The ease with w'hich the albuminoid 

 w^as broken up by the permanganate-alkali solution used in the analyses 

 strongly indicated that the greater part of the albuminoid w^as of animal rather 

 than vegeta])le origin. The broad conclusion can hardly be escaped; the 

 large amount of available plant food resulting from proximitj' to the town 

 is largely responsible for the very abundant plant grow^th; i. e. the determin- 

 ing factor is the chemical composition, particularly the nitrogen content of 

 the water. Specific statements are not so apparent. 



Fig. 11. — I'orahomas Creek, the main inlet of the LJfke. (Sec Table 8.) 



(1) Note the extreme fluctuation during March. This was due to the intermittent 

 discharge of a largo septir tank up the eour.so of the creek, and also to the alternate 

 freezes and thaws, thus influencing the drainage of .surface water from a number of farm 

 lots and pig sties above. 



(2) Total nitrogen was high. 



Note first that in all stations whether of dense or very den.se plant growth 

 the nitrate was the only one of the four compounds under consideration that 

 w^as consistenth' affected. In every graph the nitrate line fell coincident with 

 abundant plant grow^th. This w^as to be expected since the nitrate is the form 

 in w^hich the nitrogen is assimilated by the plant. Other forms were merely 

 feeders of nitrogen to the nitrate form. 



