1899] DUNE FLORAS OF LAKE MICHIGAN 301 
vent their being covered. In the moist sand at the base of the 
dune shown in fig. 9 patches of alge have been seen, presuma- 
bly Chlamydomonas, such as have been described in connection 
with the lower beach. It is doubtful if these alge are of any 
significance in the capture of dunes. 
If the vegetation gets a foothold at the base of an advancing 
slope, it tends to creep up the slope by means of vegetative 
propagation. At the base of the cottonwood dune shown in fig. 
Pe may be seen grasses which appear to be creeping up the 
‘lope in this manner. It should be borne in mind that such 
‘ppearances are often deceptive. In this particular instance the 
‘ppearance would be the same if the dune were advancing and 
% sfasses rising to keep above the sand. In like manner there 
is doubt with regard to fig. 16, as to which vegetation antedates 
the dune and which is subsequent. As has been already stated, 
“h clump of dogwoods and willows at the center beyond all 
(uestion antedates the dune; so too, the dead half-buried pines. 
The annual bugseeds toward the base, of course, are subsequent. 
The greatest doubt is as to the frost grape, Vitis cordifolia*. 
Ht the upper right hand there is a luxuriant grapevine climbing 
ue : dead pine. The clumps back of the willows and the trail- 
“8 Vines in front of them are also Vitis. Fig. 15 shows several 
age 8apevines back of the row of willows. The coarse-leaved 
ei 5 the lower right hand of fig. ro are also Vitis. It seems 
. that the vines in this last picture should be anything 
wooded A aging since the height of the sand es 
Vines are ow Is more than twenty meters. Then too tee = 
but are ‘a eo abundant all along the coast on the naked unes, 
OF insta rely found elsewhere. On the dune shown in fig. 75; 
Stowin, ok there are two willows, a dogwood, and the grape 
common és Rether. . The dogwood and one of the willows are ate 
there at mn gs adjoining swamp, while the grape was not wher 
cS. On the other hand, no grape seedlings have as ye 
Shine: any such location. While much further study 1s 
‘ . 
The identific ati but 
Prove to be thi on here may be questioned ; fruiting specimens are rather rare, 
1S Species so far as examined. 
