382 BOTANICAL GAZETTE [Mav 
shown by studying the floras of the oak and pine dunes. The 
former has a flora related to those farther south, containing 
Opuntia, Euphorbia, and many other plants of southern range. 
The pine dunes, on the other hand, show the farthest southern 
limits of many northern plants—for example, the scrub pine 
itself. Linnaea, the bearberry, and many others have a northern 
range. 
V. Conclusion. 
No attempt will be made to summarize the results of this 
study, but a few of the more striking phenomena of the Lake 
Michigan dunes and their vegetation will be given. The dunes 
have been determined in the main by westerly winds. The great 
majority of the dunes are established, and many of them are 
perched high up on bluffs. The vegetation is xerophytic, belong: 
ing either to the arctic or desert type. 
The xerophytic beaches are subdivided into three zones: the 
lower beach which is washed by summer waves and is essentially 
devoid of life; the middle beach which is washed by winter 
waves and is inhabited only by succulent annuals; the upper 
beach which is beyond present wave action and is inhabited also 
by biennials and perennials. There are also fossil beaches and 
gravel terraces with a flora resembling that of the upper beach, 
but less xerophytic. 
Perennial plants are necessary for any extensive dun 
tion on the beach, since they alone furnish growing obstacles. 
Such plants must be pronounced xerophytes and be able t 
e forma- 
. i -for- 
endure covering or uncovering. The most successful os 
: ; } nus 
mers are Ammophila arundinacea, Agropyrum dasystachyum, Eb ‘a 
pum ay 
Canadensis, Salix glaucophylla and S. adenophylla, Prunus ‘ 
Populus monilifera. Ammophila and Agropyrum form low dun 
; op 
that have a large area, because of their extensive rhizome pe 
agation. The Elymus dunes do not increase ! area Sl ; 
ease bot 
rhizome propagation is absent. The Salix dunes incr ‘cal 
in area and height, because of extensive horizontal and ‘ ce 
growth. The Populus dunes are the highest and steepest, : 
the cottonwoods grow quite tall, but do not spread horizontal’: 
