493 



Dogfish lakes) in different years tlius 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 ahundant submerged 

 vegetation is inimical to the production of plankton. 



An inspection of the planktographs in Plates VIII. -XIII. 

 and XXV.-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 Dogfish 

 lakes the autumn maximum occurs in two or three sharply 

 marked prominences, that of October 14 (3.52 and 6.60) being 

 a Melosira-SijHclKeta 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 Osci/Iaria at a time of local 

 stagnation consequent upon backwater. In 1895 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 



