422 BOTANICAL GAZETTE [DECEMBER 
the temperature of the subsoil is that of percolating water which has 
been warmed at the surface of the soil. Because of the high water- 
table and the stagnant condition of the underground water in bog 
areas, this source of heat is relatively unimportant. 
The effects of these factors, resulting in low soil temperatures, 
are far-reaching. As compared with well-drained soils, chemical 
action is retarded, the rate of diffusion, solution, and osmosis is 
greatly reduced, and the conditions for the existence of soil bacteria 
made unfavorable. Plants which can successfully compete for the 
occupancy of such areas must be able to withstand low temperatures 
and late frosts. The difference between the temperature of the air 
and that of the substratum favors plants having a low transpiration 
ratio. 
However, in so far as the region of southern Michigan is concerned, 
the temperatures prevailing in bog areas do not seem to be adequate 
to account for the presence of the bog plants or their xerophilous 
structures. It is to be noted that with the leafing-out of the trees, 
about May 27, the temperature of the maple-poplar substratum falls 
below that of the tamarack. But that the soil temperature is one 
of the factors entering into the problem of competition between 
species there can be little doubt. It is probable also that in the region 
of optimum conditions for bog plants the conditions which occur 
here only in the spring are prolonged through the summer. That 
is, the difference between air and substratum temperatures is more 
marked, and is a powerful factor in the selection of plants for bog 
areas and in the production of xerophilous structures. 
3- Texture.—This property of the substratum has already been 
referred to in connection with the genetic changes in peat. The sedge 
zone is developed upon a raft of interwoven rhizomes and roots. It 
is a coarse meshwork; but since it lies at or below the surface of the 
water, its texture is of slight importance ‘except as a means of mechan- 
ical support. As the bog develops, the admixttre of moss and shrub 
‘débris brings about'the formation of a rather compact peat, overlaid 
‘by a stratum of loose material. In: some cases, as at Delhi an 
‘Oxford, 45 miles (72*™) northeast of Ann Arbor, the living sphagnum 
makes up the bulk of this loose covering. Usually the water level 
‘lies just beneath it. As a consequence, this covering becomes the 
