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). PL XIX. — In vegetation this is the 

 richest by far of all the bodies of water examined by ns. It is 

 the type of a permanent marsh, filled from shore to shore by a 

 rank growth of plants (PI. XIX.), with little or no development 

 of channels or current, and a 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 Composita\ 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 by a 

 dense growth of the river rush {Scirpus Jluviatilis) 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 Schpus, water-lilies, and the lotus, together with great 

 quantities of the Lemnacea^ (PI. 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, is a 

 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 



