314 BOTANICAL GAZETTE | MAY 
build up a soil, and thus prepare the way for the next zone, the 
Cassandra-sphagnum vegetation. The sedges encroach farther 
on the original lake. The Cassandra-sphagnum zone makes 
conditions possible for a tamarack-spruce zone (fig. 77). Thus 
each successive zone is pushed farther and farther toward the 
center. Finally the lily center disappears, and then successively 


Fk —A general view of granite rock vegetation as seen from a granite hill 
(Sugar Loaf) near Marquette. On the margin of the lake the rocks show the first 
stages in the life-history of a forest. As the foot of the hill is approached the vegeta- 
tion becomes more and more mesophytic until a mixed conifer and deciduous forest is 
attained. Probably in places this condition is reached more rapidly because of the 
presence of glacial drift. At the top of the slopes the xerophytic condition of the lake 
border is again attained, 
the sedge and Cassandra zones, until a tamarack forest may 
come to occupy the whole territory. 
Attention has already been called to the probable factors 
unfavorable to a high development of plant life in these swamps. 
These are due in the main to undrained conditions. The accumu- 
lation of humic acids may Cause, osmotically, a drying-up effect. 
Insufficient aeration of the soil prevents a healthy growth of the 
root system of highly organized land plants, and also bars the 

