284 BOTANICAL GAZETTE [APRIL 
since the angle of slope was about 30°. The general statement 
may be made for the Dune Park complex that the maxima of 
advance are to be measured in decimeters or meters per annum, 
rather than in centimeters or decameters. No estimates can be 
given for other localities. In all probability the Glen Haven 
dunes move more slowly, since the slopes have a much richer 
vegetation. 
The height of an advancing dune above the territory in front 
of it is a very important factor, inasmuch as it often determines 
the life or death of a flora. At Glen Haven, where the advanc- 
ing dunes are from thirty to sixty meters high, no preexisting 
vegetation can survive the burial which awaits it. At Dune Park, 
where the crest is never as much as thirty meters high, vegetation 
sometimes survives. This survival is determined chiefly by the 
nature of the vegetation, and the succeeding paragraphs will 
have to do with the struggle between dunes and floras at Dune 
Park. ; 
The advancing dunes at Dune Park encroach now upon 4 
swamp, now upon a forest. Fig. 9 shows how these forest and 
swamp conditions alternate. In the right foreground is @ pool, 
surrounded by bulrushes. ‘Toward the center of the photograph 
there is a ridge tenanted by pines and oaks, then another 
swamp and another ridge. ig. ro shows a very interesting 
phenomenon. At the center is a deep trough, surrounded : 
all sides by advancing dunes. This trough has never me 
wind-sweep, but was made by the piling of the sand all oe 
The flora in this depression is not a typical ee 
g little 
Americana. Although the basswood is co 
dunes, this plant society is quite evidently a relic 
area developed under more genial conditions. 
toward the right, and the dune on that side i adv 
some degree of rapidity. The dune to the left is push 
in the main by the action of southerly winds, and m 
t of a largef 
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