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.’ per m.’), 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 XX XIII. The 
amount of plankton present from May 15 to October 1, the 
growing period of vegetation, is only 2.87 cm.’ per m.*, while 
in spring and late autumn (April 1 to May 15 and October 1 to 
December 30) it is 82.89. 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 em.*, 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, Nymphea, and Nelumbo, which die down 
and undergo considerable decay in the early fall, and (2) the 
