288 BOTANICAL GAZETTE [APRIL 
death ensues, if the rate of advance is slow. ig. 22, which 
_ represents a half buried pine that is still vigorous, was taken at 
a point where the advance is relatively slow. Figs. 15 and 16, 
on the other hand, where the pines were soon killed, represents 
one of the most rapidly advancing dunes at Dune Park. Thus 
the individual adaptation referred to in the preceding paragraph 
may be in part delusive. Perhaps the trees are able to adapt 
themselves more fully, and hence undergo a greater degree of 
covering before they die, where the advance of a dune is com- 
paratively slow. Sometimes (as in fg. rr) the territory toward 
which the dune advances is higher than the dune itself. In such 
a case the advancing dune is checked. If the entire area in 
front is higher than the dune, the sand gradually accumulates 
until the altitude is great enough to permit another advance. 
When, however, a ridge meets the advancing dune at right 
angles (as in fig. 9), the dune’s course is deflected to either side. 
If the ridge is high enough, some of the trees may be able t 
escape the fate of their associates. The pines in the background 
of fig. 17 probably represent a portion of the flora at the top of 
one of these ridges. é 
At Glen Haven, as has been stated, the forest vegetatiel 
readily succumbs, because of the great height of the advancing 
dune. The forests are mainly of two types, the maple or the 
arbor vitae. The maple forests have a dominance of gee 
charinum, and represent the most common type of mesophy ‘s 
forest in that part of Michigan. The arbor vitae forests ge 
reality swamp forests, and the most typical trees present | 
are Thuya occidentalis, Betula papyrifera, and Fraxinus Ane 
The line of dead trees along the margin of the peak 
(as shown to a slight extent in figs. rz and 12) is pat ' 
striking where there is an encroachment upon a! 
Sometimes the hemlock, Zsuga Canadensis, grows with nee 
and shares its fate. At one point the dune encront ee 
forest of Pinus Banksiana, and the results are precisely 
Dune Park. he fouttd along 
Dunes that are encroaching upon forests may DE 
