346 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



Second, we have a possible explanation of the fact that a diurnal varia- 

 tion of the free oxygen dissolved in the water of densely vegetated regions has 

 not been found to be as great or as constant as was predicted on theoretical 

 grounds. It would seem that during active photosynthesis the water would 

 contain much more free oxygen than in the early morning after several hours 

 of respiration by plants and animals in the water. But in case the free oxygen 

 combined to a considerable extent ^\nth the nitrites to produce nitrates as 

 seems indicated by the results obtained in these observations, such a large 

 variation would be prevented. 



Concerning the Ammonia Content. Not much account was taken of the 

 ammonia content, either as free ammonia or as albuminoid since no great 

 effect of the profuse plant growth could be noted upon it. Perhaps very 

 active photosynthesis would indirectly hasten its o.xidation to simpler forms 

 due to the free oxj'gen produced. It seems clear from the results obtained 

 that the ammonia acts merely as a reservoir from which nitrites and later 

 nitrates are derived. It should also be rememl^ered that aside from the am- 

 monia in solution there is always the large amount in the ooze at the bottom. 

 This would serve as a storehouse for the production of all of the compounds 

 under discussion, and would be extremely difficult of estimation. There is 

 no doubt that the bacterial action which results in higher oxidized forms 

 would be more active in the ooze than in the water. It was noticed that the 

 ammonia analyses showed great variation, and judging from the fact that 

 large amounts were found after a rough period and smaller amounts after a 

 calm, there seems to be no doubt that the variation is due to the water being 

 more or less stirred up at one time than another. It was impossible from the 

 number of analjse^ taken to arrive at any definite conclusions concerning 

 the ammonia, and since it acts merely as a storehouse, at all times well supplied 

 it seems quite unessential that further attention should be given to it in this 

 part of the paper. 



Part II. The Effect of the Nitrogen Content Upon Plant Growth. 



Attention is called to the map of Winona Lake (Fig. 10) in which the 

 regions of plant growth are stippled in proportion to the degree of density. 

 Special care was taken to get the correct pro})ortions but in spite of this the 

 shading must l^e regarded as onh' approximate. Several conditions contrib- 

 uted to the difficulty of representing on paper the amount of vegetation. 

 The following complicating factors may be mentioned; seasonal variations; 

 the impossibility of making accurate quantitative measurements of plant 

 growth per unit area; the great diversity of the growth as to species; the 

 variations in level at which the plants were found; and finally the difficulty 

 in judging the degree of shading required to represent a given condition. 



It is at once apparent from a study of the map that the regions of densest 

 plant growth are contiguous to the town of Winona Lake which is situate 

 upon and drains into the north two-thirds of the east shore of the lake. 



