304 BOTANICAL GAZETTE [ MAY 
which have passed through the first stages into mature climax 
societies. Dunes clothed with maple-beech forests are also 
found along the Michigan coast in a number of localities. It is 
difficult to understand how such a mesophytic plant society is 
attained, unless it be assumed, as observation seems to indicate, 
that by capillarity, water may rise from the ground water level 
to considerable heights in sandy soils. 
lll, THE CLAY SOCIETIES. 
There are greater difficulties in tracing the life-history of 
clay societies than of sand societies, principally because there is 
not such a perfect sequence of clay formations at the present 
time as of sand formations. With the exception of sea-cliffs 
and clearings, clay soil formations free from vegetation date 
back to the time of the retreat of the last ice sheet. Sea-cliffs, 
however, formed by the action of the waves on glacial clay, are 
a common feature along the shores of Lake Michigan. Here the 
waves are constantly undermining the cliff, and thus prevent 
anything more than a transient vegetation. But should the 
débris at the foot of the cliff become too great for the shore 
current to transport, or should a recession of the waters of the 
lake leave a cliff beyond the reach of the waves, the undermin- 
ing would cease. Here then at the outset is a clay bluff almost 
free from vegetation. 
The reclamation by plant growth begins at once. The first 
stage in the life-history is represented by herbaceous plants like 
Solidago humilis, Aster laevis, Elymus Canadensis, Prenanthes alba, 
etc. Later on xerophytic shrubs like Shepherdia Canadensis and 
Juniperus communis give a heath-like physiognomy to the bluff. 
Again, a third stage is reached in the appearance of conifers, 
poplars, and white birch. These stages are more rapid, for clay 
soil retains moisture more readily than the sandy soils. The 
action of humus on clay is exactly the reverse of its effect on 
sand, for it loosens up the soil and renders it much less soggy 
than it would be wére it free from organic decay. Where the 
cliff has been long enough freed from the action of the waves, 
