493 
Dogfish lakes) in different years thus shows that more plank- 
ton is produced in years of little, than in years of much, vege- 
tation, and tends to confirm the view that abundant submerged 
vegetation is inimical to the production of plankton. 
An inspection of the planktographs in Plates VIII.—XIII. 
and XX V.-XLII. shows the frequent occurrence of an autumn 
maximum, often well defined. In the planktographs of Quiver 
and Dogfish lakes, this autumn maximum is usually depressed 
or missing. The spring maximum occurs, as a rule, while 
the lake is full of water from the general overflow, and it is 
therefore not purely a local phenomenon. The midsummer 
and autumn plankton, on the other hand, is entirely a local 
product, and the depression of the autumn maximum must 
be due to local influences. in 1896, in both Quiver and Dogtish 
lakes the autumn maximum occurs in two or three sharply 
marked prominences, that of October 14 (3.52 and 6.60) being 
:a Melosira-Syncheta assemblage, typical for the autumn season. 
This was a year in which there was little vegetation and high 
(for autumn) water, the vegetation being, consequently, at a 
minimum as a factor environing the plankton. In other years 
this autumn maximum (see Tables VI. and VII.) is less evident. 
In 1894 the apparent maximum on September 5-6 is almost 
wholly due to the development of Oscil/aria at a time of local 
stagnation consequent upon backwater. In 1595 there was in 
Quiver Lake a maximum on September 6 (1.57), due in part to au- 
tumnal plankton and in part to adventitious organisms. Dogfish 
Lake exhibits a somewhat larger maximum (4.65) on Septem- 
ber 17, which is mainly normal in its components. The No- 
vember-December maximum of 1895 in this lake is wholly due 
to adventitious organisms, and may be disregarded in this con- 
nection. At their best, these maxima in vegetation-rich years 
are but one half to one third the magnitude of those of 1896, a 
vegetation-poor year. In Quiver Lake in 1897 and 1898 the 
autumn maximum is again depressed almost beyond discern- 
ing. Although vegetation was not abundant in the lake in 
these two years, the period of the autumn maximum was one 
