1899] DUNE FLORAS OF LAKE MICHIGAN TT 
carrying them on farther. Then, too, the driftwood may furnish 
some protection to the growing plants, especially protection from 
winds which might otherwise uproot them. Cakile and Euphor- 
bia reach their culmination on the beach, and when found farther 
inland it is chiefly on the upper beach or on windward slopes of 
active dunes. Corispermum, on the other hand, appears to be 
rather more characteristic of the active dunes than of the beach. 
Cakile is much the hardiest of the three species, venturing far- 
ther out toward the lower beach than either of the other two 
Of the three, Cakile is the most succulent and perhaps thus best 
adapted to the extreme xerophilous conditions to which beach 
plants are subjected. Euphorbia, however, has a copious supply 
of latex and its prostrate habit would seem to offer some advan- 
tages for existence on the beach. Cakile and Corispermum are 
readily dispersed by the wind, the latter by means of its winged 
seeds, while the former is a sort of tumbleweed; broken Cakile 
plants are common sights all over the dunes in the autumn and 
winter. Corispermum and Euphorbia become less and less 
common toward the north; at Charlevoix and Petoskey, Cakile 
is almost the only plant growing on the middle beach, and even 
this latter species is less common than farther to the south. 
Thus it seems as though the life conditions on the middle beach 
are more severe northward than southward, as indeed might be 
expected, 
UNIVERSITY oF CHICACC., 
[ Zo be continued.| 
