1913] COOPER—ISLE ROYALE 213 
stoloniferous species, was usually the principal mat-former, and 
Menyanthes, with somewhat similar characteristics, was next in 
importance (compare figs. 33 and 38). In those of the sedge type, 
tall stiff sedges growing in dense clumps were most important, forming 
a thick meadow-like growth. Carex filiformis was the commonest 
species, but certain areas were 
found to be dominated by Scir- 
pus caespitosus L., the most 
densely tufted of all the sedges. 
These two kinds of sedge mat 
form very different substrata for 
the growth of the sphagnum. 
On account of the shortness and 
softness of Carex limosa the moss 
is never seriously shaded where 
that sedge is dominant, and it is 
able to grow over and around the 
Carex and Menyanthes plants 
with ease. The sedges in this 
case offer no effective resistance, 
and the sphagnum soon gains the 
ascendancy over them. Where 
Carex filiformis and plants of 
similar habit are the principal 
mat-formers the moss, if it starts 
among the closely placed clumps, ec hon a 
is shaded from the beginning. It portion of a bog near Siskowit Lake: 
cannot spread laterally among Larix and Alnus incana. 
the dense clusters of thick culms, 
and so remains in a half-smothered condition until exterminated 
through the advance of the shrubs and trees. The distribution of 
the two kinds of mat-forming plants still remains to be accounted 
for, and for this I have as yet no explanation. It is entirely possible 
that the type of sedge which gains the dominant place in a given bog 
may be determined merely by accidental causes. 
Occasionally the two phases may be seen in a single bog. For 
