A STUDY OF RELATIONS BETWEEN PLANT GROWTH. 343 



(b) Regions of Extremely Dense Vegetation. 



In the two regions of- this description the vegetation was so extremely 

 dense that a boat could be pushed through onlj^ \^^th great difficulty. Great 

 stagnation existed in lioth places. The water in station T at the place where 

 the samples were taken was .3M deep. The station was well protected as 

 its location on the map will show. The water in the other station of this 

 description, the canal, was about IM deep. 



The plant growth consisted mainly of various pondweeds, Potamogelons; 

 waterpest, Elodea canadensis; duckweed, Spriodela polyrfvka; eel grass, 

 Vallisneria spiralis; Naiasflexilis;&[a,uientous and confervoid algae, and phyto- 

 plankcton. The algae predominated in the canal while the phanerogams 

 constituted the main bulk of the plants in station T. 



Nitrate Behavior. In each ease the stations showed a rapid fall in nitrate 

 and then remained low, in fact extremely low, tliroughout the remainder of 

 the season. The reason for the fall in content is apparent in the light of the 

 great drain that such a dense vegetation would make upon the nitrate in 

 solution. In this connection, it should be remembered that the water could 

 circulate very little due to the resistance offered by the mat of plants. The 

 water in this station was also quite shallow, as before stated, and hence could 

 hold no great store. 



Nitrite Behavior. The behavior of the nitrite in these stations is peculiar 

 but very significant. As has been stated before, the nitrite was very low at 

 the end of winter as the ice was going off. It then gradually rose until April 

 20 at which time it began to show a rapid rise, due no doubt to the fact that 

 while at that time the higher plants has been unable to get a start, the bacteria 

 on the other hand had flourished inordinately. Toward the latter part of 

 June the phanerogams began to flourish and much free oxygen was produced 

 as a by-product of photosynthesis. The effect of this was to oxidize the nitrite, 

 and hence the precipitous fall of nitrite from June 24 to July 12. 



The conditions in these regions remained more uniform than in regions 

 of less plant growth, due I think, to the fact that large amounts of algae and 

 phytoplanctou were found in these regions and this tended to keep the vegeta- 

 tive processes in the ascendency, which was not the case in the regions of less 

 density. The temperature of the water was high, due to the fact that there 

 was little interchange with other regions, and to the fact that the water 

 was shallow (100° F was frequently reached and temperatures as high as 

 106° F were observed). The presence of so much free oxygen, a high tem- 

 perature, a high bacterial count, and a nitrate content which remains low, 

 due to the constant drain upon it, results in the oxidation of the nitrites 

 almost as soon as they are formed. 



Tivo Points of Interest outside the scope of this paper to be noted at this 

 point are: 



