494 



of prolonged low water in both years, so that whatever vegeta- 

 tion was present occupied relatively a large proportion of the 

 area and volume of the lake, especially as contrasted with the 

 conditions in 1896. The available data thus indicate that veg- 

 etation is inimical to the production of plankton, as shown not 

 only in the general averages but also in these maxima, which 

 may be regarded as the expression par excellence of the produc- 

 tive capacity of the lake. 



There still remains for consideration, with reference to the 

 effect of vegetation upon plankton production, the result of 

 our examination of Flag Lake. As before stated, this is a 

 marsh choked with a rank semiaquatic growth whose extent, 

 abundance, and relative occupation of the area of the lake 

 equals or exceeds that in any other body of water examined by 

 us. If our thesis that vegetation is inimical to the production 

 of plankton be true, we might expect to find here, of all places, 

 barren waters. This is not, however, the case ; for, as shown in 

 the table of comparison of plankton production on page 429, 

 Flag Lake is very productive (11.46 cm. 3 perm. 3 ), being ex- 

 ceeded only by Phelps Lake (19.65). 



The only indication that vegetation is in the least inimical 

 to the plankton in the lake is suggested in Plate XXXIII. The 

 amount of plankton present from May 15 to October 1, the 

 growing period of vegetation, is only 2.87 cm. 3 per m. 3 , while 

 in spring and late autumn (April 1 to May 15 and October 1 to 

 December 30) it is 32.89. In Phelps Lake, which, save for vege- 

 tation, is much like Flag Lake, the plankton during the period 

 of dominance of vegetation in 1896 averages 7.64, and in 1898 

 52.43 cm. 3 , 3 to 18 times as much as in the vegetation-rich 

 waters of Flag Lake. 



In the character of the vegetation in Flag Lake lies, I be- 

 lieve, the explanation of its fertility in plankton. Two kinds 

 are predominant, neither of which is present in like abundance 

 in Quiver Lake. These are (1) succulent vegetation, such as 

 Sagittaria, Pontederia, Nymphcea, and Nelumbo, which die down 

 and undergo considerable decay in the early fall, and (2) the 



