386 
of the year reduces greatly the value of the data for such pur- 
poses or for comparison with other localities. 
The hydrographic conditions are such in 1896 that this lake 
maintains, throughout, a connection with the river. This is 
owing to the relative absence and brief duration of low levels, 
the run-off not being completed before a new invasion occurs 
asa result of a recurrent flood. Since falling levels prevail 
during more than two thirds of the year, a run-off from the 
lake continues during this portion of the timeat least. The 
lake is therefore in this year a factor in the determination of 
production in channel waters, whose continuity is broken only 
when levels are such that no waters are draining off from the 
lake or passing through it during general overflow—which is the 
case in less than one fourth of the time. The average produc- 
tion in the lake for 1896 (18.83) is almost twelvefold greater than 
that in the stream (1.16), and the monthly averages also (see 
table between pp. 342 and 343) are from 24 to 218 times greater, 
while individual collections in the lake in all but three in- 
stances exceed coincident or approximate ones in the river. The 
exception on July 30 occurred, when the invasion of flood water 
was followed, as is usually the case in midsummer in vegetation- 
rich backwaters, by a semi-stagnation with great development 
of Oscillaria, and the formation of considerable gas with a strong 
odor of H.S beneath the felt of Oscillaria which covers the bot- 
tom. Under these presumably abnormal conditions the plank- 
ton content reached a lower level in the lake (1.62) than in 
the river (3.90), and this was at a time of influx rather than 
outflow of water. With the above exceptions the lake at all ob- 
served seasons contains a richer plankton than the channel, 
which its run-off directly enters,and under similar hydrographic 
conditions we are justified in predicting at other times a similar 
relationship, though the exact ratio of production would proba- 
bly vary according as the vegetation by its growth or decay 
affected the fertility of the water. 
In the absence of any satisfactory basis for determining 
the amount of the run-off from this lake, a quantitative expres- 
