245 
eastern border and the encroachments of the semiaquatic bot- 
tom-land plants but slightly vary the uniformity of the vegeta- 
tion, which at low-water stages fills the greater part of the lake. 
In such lakes as Dogfish and Quiver the vegetation by 
reason of its predominance exerts a profound influence upon 
the quantity and the constitution of the plankton. Its fluctua- 
tions in quantity with the change of the seasons and the inva- 
sion of flood water are attended by marked readjustments of 
the plankton. 
Phelps Lake (Station F'), Pl. XXI.—Phelps Lake was prac- 
tically free from vegetation throughout the period of our plank- 
ton collections. The drying up of the lake in 1894 and its cul- 
tivation in 1895 destroyed whatever foothold the aquatic veg- 
etation had obtained. In the following years the ingress of the 
aquatic flora become increasingly evident, though the alluvium 
in the bed of the lake, hardened by the drouth, gave but scant 
foothold to marsh-loving plants, especially to the perennial 
species or to those with well-developed roots. Each spring saw 
here a remarkable development of “blanket moss,” a mat of 
alge, principally Spirogyra, Zygnema, and Cladophora. In the 
period of midsummer stagnation a dark green film of Oscillaria 
coated the bottom or rose to the surface in scattered masses. 
The fringe of button-bush (Cephalanthus occidentalis) and 
willows (Salix nigra and S. longifolia) at the edge of the sur- 
rounding forest gave shelter to a few semiaquatie Composite and 
rushes, and beyond these there were scattered clumps of Pota- 
mogeton natans and Nais flexilis var. robusta, which found a 
place even in the first year in which the water reentered the 
lake. In 1899 the margin occupied by these plants had increased 
in width, and arrowleaf and lotus were represented by a few 
isolated plants, while the ubiquitous Ceratophyllum had made 
its first appearance in the lake. Aside from the alge, the aquatic 
flora formed but a small part of the environment of the plank- 
ton in this body of water. 
Thompson’s Lake (Station G). Pl. XX.—This lake combines 
in one area almost the whole range in the development of the 
