309 
though the invasion resulted in the enrichment of the lake by 
the decay of vegetation and dead animals. It may also have 
“seeded” the lake with organisms whose subsequent multipli- 
cation caused these temporary increases in production. These 
same floods are attended by depressions in production in the 
main stream, so that these two pulses in Quiver Lake lie in 
these depressions, intercalated between summits of the curve 
of production in channel water (cf. Pl. IX. and XXVI.). The 
inference is suggested that the run-off of this plankton-breeding 
impounded water of Quiver Lake and similar reservoirs else- 
where may have contributed to the increased production in 
channel waters following the flood. 
The plankton content of Quiver Lake water on July 26 
(.71) and Sept. 6 (1.57) thus exceeds that in the river on July 23 
and Sept, 6 (.68 and .99), and its contributions to the stream, if 
any were made, serve to enrich the channel plankton. In three 
other cases the lake production exceeds that of the river; on 
Feb. 23 (lake, .03, river, .01), April 9 (1.42 and .52), and Dec. 28 
(.29 and .01). In the first instance there was stagnation under 
the long continued ice-sheet in both river and lake, as wasshown 
by the great mortality of fish in the latter. The plankton, how- 
ever, did not reach the degree of extermination in lake water that 
it did in the channel, since there was less sewage, more veg- 
etation, and access of spring water. In the April instance 
the silt burden of the channel waters (4.67 cm.’, Pl. IX.) 
is much greater than that in the lake (1.43), and suggests the 
intercalation of storm water in the former, resulting in the 
slight rise in levels (PI. IX.) andthe lessened plankton content 
of the channel waters as compared with those of the less dis- 
turbed lake. The great contrast on December 28 is also due 
to the flushing action of the great winter flood which depleted 
the channel plankton but increased the impounding function, 
and therefore breeding capacity and productivity, of the lake. 
Each of the three instances of greater production in lake than 
in river waters occurs with rising river levels, when the rising 
river checks the relative outflow from the lake or otherwise 
