A STUDY OF RELATIONS BETWEEN PLANT GROWTH. 341 



C. Littoral Regions Where Phanerogams Grew so Dense that the 



Circulation of the Wind Driven Currents was Inhibited 



or Wholly Prevented. 



(a) Regions of Dense Groivth. 



Stations A, B, R, P and Q answered to this description and from them the 

 follo^ving data were taken. They are readily located on the map (Fig. 1). 



Nitrate Behavior. In these stations nitrate fell very rapidly during the 

 last of June and the first few days of July. All stations agreed in this respect, 

 as is shown by Fig. 7, which also shows the five graphs from the South Bay 

 stations. After July 5, the nitrate content seemed to have come to a state of 

 equilibrium and was produced and used at about the same rate. The ex- 

 planation of the nitrate curve is rather simple. The bacteria increased very 

 rapidly during the warm days of spring and produced a great surplus of 

 nitrate before the plants got fairly started. Then the plants being supplied 

 with abundance of plant food and bright sunshine grew apace and succeeded 

 in cutting down the surplus of nitrate and early in July established nitrate 

 equilibrium at a rather low level. 



Nitrite Behavior. The nitrite content fell gradually until about July 5, 

 remained low until July 19 after which it gradually rose until the last analyses 

 were made (Aug. 3). The explanation of the first part of the nitrite curve is 

 no doubt similar to that for the nitrate of the same time. Then during the 

 folloAving period of low content, photosynthesis was extremely active due to 

 the bright sun and warm weather. 



This resulted in a supersaturation of free oxygen in the water, as was 

 evidenced by the fact that bubbles of oxygen were seen over the surface of 

 the plants. The then existing conditions would facilitate the passage of 

 nitrites into nitrates as will be further discussed under the conditions existing 

 in regions of extremely dense plant growth. 



Following this period the reproductive processes predominated over the 

 vegetative and hence the amount of free oxygen produced by photosynthesis 

 was reduced and the amount used for respiration was increased with the end 

 result that the amount of free oxygen in the water considerably lessened. 

 At this time the nitrites began to increase due to the fact that less was being 

 converted into nitrate. This result was noted in all of the stations considered 

 in this division, and was also noted in the five stations in South Bay and in 

 the lake body itself indicating that the process was general rather than local. 



Confirmatory evidence of the above explanation is found in the fact that 

 during the latter part of July and the whole of August, the vegetation was 

 much paler than earlier in the season, and the plants were mainly engaged in 

 producing flowers and fruit, rather than vegetative growth. Katabolic 

 processes using free oxygen probably predominated over anabolic processes 

 producing free oxygen. 



