432 BOTANICAL GAZETTE [DECEMBER 
herbs gradually are superseded by a growth of Larix. This society 
has been much disturbed by lumbering, and a large part of the 
original area has been cleared. But there is good evidence to show 
that the part of the basin filled with peat formerly supported a dense 
covering of tamaracks. Where best developed and least disturbed, 
it shows an undergrowth of Vaccinium corymbosum, Aronia nigra, 
etc. As the other species are practically the same as at the lake to 
be described next, they need not be enumerated here. In contrast 
with most of the areas studied, the almost complete absence of 
sphagnum is worthy of note. It is also important that the absence 
of any gradation between the forest societies of the upland and of the 
bog be kept in mind. 
On this lake, then, there are two divergent series of plant societies. 
Starting with practically the same species, the one series leads us 
on mineral soil through willows, maples, and elms to the oaks of the 
surrounding forests; the other, owing to the development of a floating 
substratum, involves a very different set of shrubs and ends with the 
tamarack. The former series therefore more closely approximates 
the climatic type, while the latter is dependent upon edaphic factors. 
FIRST SISTER LAKE. 
This lake and its accompanying bog are located three miles west 
of Ann Arbor in a glacial drainage valley. Its origin is probably 
connected with the melting of a mass of stagnant ice after the 
abandonment of the valley by glacial drainage. The surrounding 
and underlying soil is a sandy gravel. At least a part of the western 
side presents an original tamarack bog vegetation, and it is particu- 
larly interesting in showing the results of competition between bog 
plants and those of other habitats (fig. 6). The vegetation in general 
Presents a different phase of the bog societies, as compared with 
West Lake. Especially to be noted are the dominance of cassandra 
and sphagnum in the shrub zone, the absence of cattails and swamp 
loosestrife as important members of the outer margin. The tamarack 
zone is also raised somewhat more above the water level. 
Aquatics.—With the exception of the shallow-water forms, the 
lake is almost free of higher vegetation. Potamogeton lucens and 
P. zosteraefolius occur sparingly. About the margin, however» 
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