249 
ble periods of time the vegetation forms no appreciable part of 
the environment of the plankton. It was in this region that 
the most of our collections were made, and they may therefore 
be regarded as in the main typical of vegetation-free waters 
of our locality. 
Flag Lake (Station K). P\. X1X.—In vegetation this is the 
richest by far of all the bodies of water examined by us. It is 
the type of a permanent marsh, filled from shore to shore by a 
rank growth of plants (Pl. XIX.), with little or no development 
of channels or current, anda bottom of ooze with great quanti- 
ties of decaying vegetation. The wide expanse of this marsh 
(over 1,200 acres) and the varied character of its borders afford 
opportunity for great diversity in its vegetation. Its margins 
are not sharply defined, and the vegetation in such regions 
varies greatly according to the locality, and in the same local- 
ity according to the present and previous stages of water. Thus 
in the autumn of low-water years the Composite, Polygonums, 
and grasses of the dry and higher bottoms attain a rapid and 
rank growth in regions where Sagittaria and Lemna held sway 
in the spring. A greater part of this marsh is occupied bya 
dense growth of the river rush (Scirpus fluviatilis) to the exclu- 
sion of almost all other aquatic species of any size. Here and 
there irregular areas of considerable extent are filled with scat- 
tered Scirpus, water-llies, and the lotus, together with great 
quantities of the Lemnacew (Pl. XIX.). Near the center of the 
marsh there existed throughout the years of our examination 
two irregular spaces of open water of several acres in ex- 
tent, more or less encroached upon by a surrounding belt of 
Ceratophyllum. Whenever access was possible our collections 
were made in these open places. 
The vegetation of this marsh, by reason of its omnipres- 
ence, its great volume, and its periods of growth and decay, isa 
factor of great importance in the environment of its plankton. 
The nourishment taken up by the submerged and more succu- 
lent vegetation is released again by decay in the autumn, and 
thus favors the development of the autumnal plankton. The 
