352 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



When the above symbols are enclosed in parenthesis () they indicate 

 that the conditions represented existed just previous to the time of taking the 

 sample. In case a number is enclosed in the parenthesis it means that the 

 represented conditions have existed for that many days. 



Illustration of the use of the symbols : 



Cmh(10)vv means clear, calm, hot, at the time and for the ten days 

 just preceding, very dense vegetation. 



Ctn(dxr)o means clear, ripples, moderate temperature, at the time sample 

 was taken and that the period preceding was dark, cool, and the lake rough; 

 no vegetation found in that particular station. 



The following arbitrary signs are used in recording the data also. 



* after an analysis means it was checked for accuracy. 



??? means that an analysis was doubtful and hence rejected. 



means that no attempt was made to determine the amount of the 



particular comjjound in question. 



The nitrite for Station F is very similar to that for Station T (Fig. 8.) 



Also as in P"'ig. 13, the region of greatest plant growth M^as the region of 

 lowest nitrate content. 



Vegetation was rapidly increasing during the time covered. 



(1) Note the great difference in nitrite at different dates in the ease of 

 Station T. 



(2) In each case tlie r(>gion of greatest ])lant growili is the region of lowest 

 nitrate content. 



(3) Nitrate estimate in analysis 109 is ])rol)abIy an error, l)eing too high. 

 Analysis 109 was one of the very few of the last one hundred analyses which 

 was unchecked for accuracy. 



(4) The amount of vegetation increases rapidly from June 28 to July 26. 



(5) In the following three graphs the horizontal spaces have no time 

 significance. The grouping is entirely arbitrary and merely a matter of con- 

 venience. 



(1) Note that altho tlie grapli for nitrite is nearly straight, in every 

 case save that for July 5 it describes a very much flattened out letter M. 

 This seems more than accident, and considering the slight differences is 

 surprising. Note too that an error of .01.") parts per million would l)e all that 

 was necessary' to spoil tlie figure even in that case (July 5). 



(2) Note that the nitrites gradually ascend in relation to the nitrates. 



(3) The points indicated in (1) and (2) indicate that a ilelinite relation 

 exists between the stations and that these relations remained quite constant 

 even while the group relations changed as time i)rogressed. 



