384 BOTANICAL GAZETTE [way 
which dunes are advancing. While most of the vegetation is 
destroyed at once, Salix glaucophylla, S. adenophylla, and Cornus 
stolonifera are able to adapt themselves to the new conditions, 
by elongating their stems and sending out roots from the 
buried portions. Thus hydrophytic shrubs are better able to 
meet the dune’s advance successfully than any other plants. The 
water relations of these plants, however, are not rapidly altered 
in the new conditions. It may be, too, that these shrubs have 
adapted themselves to an essentially xerophytic life through liv- 
ing in undrained swamps. Again it may be true that inhabitants 
of undrained swamps are better able to withstand a partial 
burial than are other plants. 
Vegetation appears to be unable to capture a rapidly moving 
dune. While many plants can grow even on rapidly advancing 
slopes, they do not succeed in stopping the dune. The move- 
ment of a dune is checked chiefly by a decrease in the available 
wind energy, due to increasing distance from the lake or to bar- 
riers. A slowly advancing slope is soon captured by plants, 
because they have a power of vertical growth greater than the 
vertical component of advance. Vegetation commonly gee its 
first foothold at the base of lee slopes about the outer margin of 
the complex, because of soil moisture and protection from the 
wind. The plants tend to creep up the slopes by vegetative prop 
agation. Antecedent and subsequent vegetation work together 
toward the common end. Where there is no antecedent veget# 
tion, Ammophila and other herbs first appear, and then a dense 
shrub growth of Cornus, Salix, Vitis cordifolia, and Prunus ih 
Siniana. Capture may also begin within the complex, as 
in protected depressions, where Sa/ix longifolia is often abundant. 
Tilia Americana develops rapidly on the captured lee slopes; 
and the thicket is transformed into a forest. The trees ae 
densely, and there is little or no vegetation carpet. Associate 
with Tilia is a remarkable collection of river bottom plants, *° 
that the flora as a whole has a decided mesophytic cast. eae 
plants have developed xerophytic structures that are not ee 
in the river bottoms. Acer and Fagus succeed Tilia and rep 
