402 BOTANICAL GAZETTE [DECEMBER 
Salix discolor, Acer rubrum, Ulmus americana, and Fraxinus 
americana. 
While it often happens that locally the one occurs only in 
drained conditions and the other only in undrained situations, 
field work carried on over any considerable area will show that 
drainage conditions are not adequate to account for the presence 
or absence of either of these two distinct types of vegetation. 
The presence of peat, with the consequent accumulation of humus 
acids, has been commonly spoken of as preventing the coming 
in of the “drained swamp”’ types. In southern Michigan and 
northern Indiana, however, there are many swamps with a thick 
substratum of peat and without an outlet, yet supporting a vege- 
tation made up wholly or in part of these plants. It is true, 
however, that the bog societies occur here only in poorly drained 
situations, underlaid with peat or bogus soil. 
Again, it is not unusual to find these two society groups grow- 
ing on opposite sides of the same lake, where the underlying soil 
can be shown to be the same. To account for this, it has been 
suggested that the depth of water in the two situations is of im- 
portance. But any ideas of this kind can be disproved by car- 
rying the criteria into a new locality. Just to the west of Ann 
Arbor, Mich., occurs a small glacial lake. This was formerly 
surrounded by a quite typical group of bog societies. Within 
recent years the eastern side of the lake has been entirely cleared, 
and a large part of the original tamaracks on the south and south- 
west sides have been cut away. There is left a rather pure 
growth of bog plants on the northwest side. Since the clearing 
was made on the southwest side there has sprung up a dense 
growth of herbs, shrubs, and trees, nearly equaling in height the 
adjoining grove of tamaracks. But if we note the species pre- 
vailing in this area, we find the plants enumerated above as typi- 
cal of drained swamps. It is practically impossible to account 
for this situation on the basis of soil difference, chemical char- 
acter of the soil solution, drainage conditions, or depth of water. 
In his paper on the ‘Physiographic Ecology of Chicago 
and Vicinity” Cowles? distinguishes one “drained” and three 
? Bot. GAZ. 31: 145-155. 
