52 BOTANICAL .GAZETTE [JANUARY 
3. Since their separation the physical characters of the two 
lakes have become very different, leading to marked differences 
in the character of their plankton. 
4. These differences appear to be due primarily to the greater 
depth of the second and the more rapid filling of the basin of 
the first lake. The reasons for the latter are not clear. 
5. A luxuriant flora probably flourished on the terminal 
moraine at the time of retreat of the ice sheet. The lake was 
first invaded by aquatic and amphibious plants. As humus 
accumulated, there followed in turn sedges and sphagnum, 
shrubs, a pure tamarack, and then a mixed, soft-wood, decidu- 
ous forest. 
6. Vegetation accumulated faster on the western than on the 
eastern side of the lake, due at least in part to the direction of 
prevailing winds. The ax, fire, and pasturage have obscured the 
order of succession in some places and prolonged the period 
required for the ultimate reclamation of the basin. Other causes, 
not yet sufficiently investigated, have resulted in marked differ- 
ences in composition of the bog floras of this and neighboring 
lakes, and in the constitution and rapidity of formation of the 
vegetable substances with which they are becoming filled. 
UNIVERSITY OF MICHIGAN, 
