386 BOTANICAL GAZETTE [May 
results obtained from this study show that the vegetation pro- 
foundly modifies the topography. In like manner the flora has 
often been studied from a purely taxonomic standpoint, little 
attention being paid to the striking effects of the environment 
upon plant structures. More recently the ecological standpoint 
has been taken by a number of investigators, particularly to 
show the influence of the extreme environment upon plant 
organs and tissues. The second part of this paper will treat this 
phase of the subject in some detail. Very little previous work 
has been done on the geographic phase of the subject from the 
standpoint of historical development and the order of genetic 
succession of the various dune types. Still less has there been 
any adequate study of the modifying influence of vegetation upon 
topography. These latter phases of the subject have given color 
to the work which has resulted in this paper. 
Warming’s work on the sand dune vegetation of Denmark 
stands in the front rank. In his separate publications and in his 
text-book of ecology, the conditions on the Danish dunes are 
quite fully stated. The order of succession, speaking broadly, 
seems to be quite similar to that along Lake Michigan, but there 
appears to be less diversity of conditions, and the features appear 
to be developed on asmaller scale. The strand is succeeded by 
the wandering or white dunes, and these by the established or 
gray dunes. Beyond these are sandy fields. Just as along Lake 
Michigan, the dune floras may pass into the heath and these 
latter into coniferous forests. 
There is a remarkable similarity in the flora of the Danish 
and Lake Michigan dunes. The same genera and often the same 
species occur in the two regions. Cakile maritima and Lathyrus 
maritimus grow on the strand. Ammophila arundinacea (==Psamma 
arenaria), Elymus arenarius, and A eropyrum junceum grow on the 
wandering dunes. Where the genera are not common OF ow 
nearly related, there are to be found in the two regions plants 
that have the same life habits. There is thus a striking similar- 
ity in the two regions in almost every respect, and that too M 
spite of the marine conditions in Denmark, as contrasted with 
