369 
In 1895 the lake was choked with vegetation which the 
winter flood largely removed and the recurrent floods of the 
following year reduced somewhat in extent, while higher levels 
lowered its relative occupation of lake waters. 
PLANKTON PRODUCTION, 
1895. 
(Table VI., Pl. XXX.) 
There were 12 collections in this year, from April to De- 
cember, averaging 3.25 cm.* per m.’ The average of the 
monthly averages (see table between pp. 342 and 348) is 3.3 
em.* to .74 and 6.65—similar averages for the same period in 
Quiver Lake and the [Jlinois River. The maximum collection 
was made Dec. 19—a very unusual date for such production. 
A superposition of the planktographs of the river and 
Quiver and Dogfish lakes for this year brings out some in- 
structive similarities and differences in the movement of pro- 
duction. The vernal pulse of April 29, in so far as the data 
reveal it, is quite similar in all three localities, reaching its 
greatest development in Dogfish Lake (8.20), where im- 
pounding action is greatest, and being greater in the river (5.83) 
than in Quiver Lake (4.57), where, owing to low levels, the 
proportion of water of recent creek or spring origin is greater 
than in the channel of the adjacent river. 
The June-July pulse may be found in all three localities, 
but it is belated and much smaller in the lake waters. This 
pulse in Dogfish Lake (4.59 em.* per m.*) is less than a sixth of 
that in the river (30.42), where, in the semi-stagnant sewage- 
polluted channel waters of unusually low levels, Moina and 
other Cladocera caused the unusual production. Between the 
April and June-July pulses the river levels fell 2 ft., to mini- 
mum stages (Pl. XXX.), so that the proportion of creek and 
spring water in Quiver Lake is probably more than doubled at 
the later date. This may account in large part for the very 
low production in Quiver Lake (.02) on July 8, while on July 5 
