415 
makes its way through a now abandoned channel to the lake 
and thence out to the river through the slough. Below this 
level, the current of the gentle run-off of the great tract of adja- 
cent impounded backwaters with which this lake has then but 
a slight connection is the only movement in the area. 
The surrounding bottoms are heavily wooded for a narrow 
margin along the lake, though the forest gives way to cultivated 
fields on both sides within a short distance. Its bottoms and 
shores are of a rich black alluvium, which in low-water seasons 
such as 1895 becomes the soil of a cultivated field. 
The vegetation of this area is unique among our plankton 
stations in its character and relation to the plankton. In 1894 
there was little vegetation present, and whatever aquatic 
growth had gained a foothold was eradicated by the dry au- 
tumn and by the cultivation of the soil in 1895. In 1896-1899 
the occupation of the lake by water was more continuous, and 
Potamogetons, Naias,and even Nelumbo, gained a slight foothold 
along the margins. The principal vegetation was a dense mat 
of filamentous green alge, such as Spirogyra and Zygnema, 
which covered the margins for a considerable distance into the 
lake. During the heated term of midsummer a dense felt of 
Oscillaria covered the bottom of the lake everywhere at times. 
These algz were present during most of the summer, though 
most abundant in spring, and by their continuous and prompt 
decay they release into the lake waters a volume of nitrogenous 
and other substances which are utilized by the phytoplankton. 
The cumulative action of the longer-lived aquatic phanerogams 
in withdrawing from the lake large stores of food which are 
again released in the ensuing autumn or spring by the decay of 
the season’s growth, is thus quite absent from this body of wa- 
ter. The rapidly growing and rapidly decaying alge permit a 
repeated flux of nitrogenous and other substances utilized by 
the plankton as food in the course of a single season. This fac- 
tor, combined with the complete impounding function of this 
lake below river levels of 8 to 9 feet and the absence of tributary 
and spring water, is, I believe, the secret of the unusual plank- 
ton production in this area. 
