68 Postelsia 
at slight elevation above the lake level. 
bs Nird™beach: 
Within this zonal region of the beach, the 
lakeward and shoreward influences meet and 
commingle in such a way as to call forth the 
greatest complexity of conditions. As the forest 
is approached the influences of the lake decrease, 
and in hke manner as the water 1s neanedmse 
those of the forest become of less weight. The 
optimum is therefore established somewhere in 
the middle zone. Besides the transitions in the 
societies undergone in passing from the front 
towards the back, one also notes changes in the 
longitudinal direction of the strand like those of 
the front beach in passing from low and mucky, 
to raised sandy beach and stream delta. This 
longitudinal transition results in the division of 
the midstrand vegetation into societies more or 
less distinct and conditioned by the soil com- 
position. The sandy beaches show a greater 
variety of species than the low humus ones, but 
fewer individuals im a given area. ~ Whismais 
largely due to the fact that there are more typ- 
ical turf builders, sedges and the like, found 
