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, Nymphcea, and Potamogeton natdns. 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 immersed and 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 

 Dogfish 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- 



