251 
ized by Chara—called the Characetum—is entirely absent in our 
locality. The zone characterized by pond weeds—Potamoge- 
tonetum—may perhaps be found in the great areas of immersed 
vegetation, principally Ceratophyllum, which occur in Quiver 
and Thompson’s lakes. The few Potamogetons found in our 
locality occur in this zone, though they are not confined to it. 
The depths in which this zone is here found are much less than 
in Lake St. Clair, in the lacustrine environment. The “Nu- 
pharetum” may be represented in the lotus beds of Quiver, 
Thompson’s, and Flag lakes; but these do not show a zonal 
arrangement, and merge variously with littoral and Ceratophyl- 
lum regions. The littoral zone, which, according to the authors 
above quoted, extends from the shore line to a depth of 3 me- 
ters, is confined in our waters to a much shoaler region, and, as 
elsewhere, is characterized by Scirpus, the sedges, Polygonum 
amphibium, Nymphea, and Potamogeton natans. Almost all of 
Flag Lake, the northern and southern ends of ‘Thompson’s Lake, 
and the northern and eastern margins of Quiver Lake belong to 
this zone. 
A classification more applicable to our locality is that of 
Pieters (’01), who recognizes in Lake Erie two regions,—one 
including all submerged forms and those with floating leaves, 
the other all the remaining species with emersed leaves 
and growing with roots and parts of the stem in the water.” 
These regions of immersedand emergent flora are often recogni- 
zable in our locality. To the latter belong the greater part of 
Flag Lake, a considerable portion of Quiver Lake along the 
eastern and northern shore, and the two ends and the margin 
of Thompson’s Lake; to the former, the body of Quiver and 
Dogtish lakes, a small area in Flag, and a large area at either 
end of Thompson’s Lake. — It is this zone which constitutes the 
great plant factor in the environment of the plankton of our 
waters, and it consists almost entirely of Ceratophyllum. The 
effect of vegetation upon the production will be discussed in 
another connection. 
It is evident that our investigations afford a unique oppor- 
