200 BOTANICAL GAZETTE [MARCH 
‘dune-former, and fig. 5 shows a group of cottonwoods on an 
embryonic dune partially buried by the sand. Photographs 
might have been secured showing trees, presumably fifteen meters 
in height, buried up to the topmost branches and yet alive and 
vigorous. Fig. 8 (taken in the winter) shows a vigorous clump 
of trees, high up on the dune-complex, with their roots exposed 
by reason of the removal of the sand from around them. Much 
more striking examples than this have been seen of living trets 
standing high up in the air, and yet with no apparent injury. In 
one respect the cottonwood is a hardier plant than Corispermum; 
it is a perennial and hence passes the winter on the dunes, In 
the summer the winds are much more moderate, and the chances 
of being covered or uncovered are more remote. 
Two grasses are more or less at home at many plac 
complex, Ammophila arundinacea and Calamagrosts longifolia. 
Of these the latter is the hardiest and most typical of && 
positions, such as shown at the left in fig. 23. The tenacity 
which Calamagrostis holds its ground has already been meh 
tioned. On the Glen Haven complex, Ammophila is particularly 
abundant. In some places it is so thick and green as to | 
almost like a field of grain from a distance; yet even here, 
luxuriant growth is only in the protected places, and none at 
is found in the most exposed situations. 
The reasons for the scanty plant life on the exposed regi 
of the dune-complex are not far to seek. First of all it 1s 
~ due to the scarcity of water in the soil. Even after a long agit 
of drought in summer, the sand is cool and moist at a short : 
tance below the surface. The upper dry layers of sand “ 
non-conductor of heat and prevent the evaporation of the w4 4 
that lies beneath. The height of the underground water le 
beneath the dunes was not ascertained. Indeed it is ' 
necessary to determine where this level actually resides, 8 
there is enough water far above it to support 4 luxuriant vege 
tion, if that were the only factor concerned. 
In spite of the water supply in the dun 
flora of the complex is characterized by the 
es on the 
with 
the 
e sand, the x be 
“possession 4 
