428 BOTANICAL GAZETTE [DECEMBER 
(3). Furthermore, it has been shown that when soil rich in nitrogen 
is saturated with water so as to exclude free oxygen, denitrification 
takes place and nitrogen gas is set free (29, p. 115). 
The phosphoric acid content is comparable with that of the best 
soils, and it is at least partially in a condition for plant use. 
The potassium content is very low. Analyses and the results 
of agricultural experiments show that in order to produce crops this 
substance must be added, and preferably in an alkaline form. Inquiry 
among the owners of onion marshes in this vicinity confirms the need 
for potassium in local bog soils. 
The amount of calcium present is reported as equal to that of 
the best upland soils. But it is probable that as ‘it exists under 
natural conditions in bogs it is bound up largely in insoluble humates. 
Under the influence of oxidizing processes it would become available 
to the plants at the surface. 
When we consider the conditions under which the various plant 
societies in our bogs exist and their competition with one another, 
there can be little doubt but that the substratum varies in each case 
as to its chemical composition. ‘That the societies may be classified 
on a physiographic basis is certain, but how to determine the chemical 
factors accompanying each physiographic change is an unsolved 
problem. The ordinary methods of analysis give us the minerals 
present, but tell us little about their form and availability for plant 
assimilation. The colorimetric methods for determining the quantity 
of mineral salts present in bog water are mostly open to objection. 
The ease with which the humous bodies of the bog water are decom- 
posed render their quantitative estimation by present methods of 
little value. Yet it seems probable that work upon the chemistry 
of humus and humous compounds must result in data valuable alike 
to the ecologist, the forester, and the agriculturist. 
C. Broric ractrors.—The interrelations of the bog species will 
be discussed in connection with their other ecological characters. 
It will be sufficient to mention here that they are with a few excep 
tions light-demanding forms. Consequently, size and ability to 
produce shade are the important factors in their competition with one 
another. 
A second element enters into this problem of the struggle between 
