306 BOTANICAL GAZETTE . [APRIL 
tion within the dune-complex. Of course all antecedent vegeta- 
tion has been long ago destroyed. The capture of the dune 
must, therefore, be effected entirely by means of plants which 
germinate and develop on the complex itself. Speaking broadly, 
_the complex is almost entirely composed of windward and lee- 
ward slopes. Since the windward slopes are low, it follows ’ 
that they cover a much larger area than do the other. Perhaps 
nine tenths of an ordinary dune-complex is directly exposed to 
the prevailing wind. The capture of any portion of the wind- 
ward slope is unlikely, because of the combination of exposure 
and instability of soil. In the summer a somewhat extensive 
vegetation may develop, made up largely of annuals and bien 
nials. The most abundant of these plants is Corispermum hyss0- 
pifolium. Other species are Artemisia Canadensis (or A. caudata), 
Cakile Americana, Euphorbia polygonifolia, Cnicus Pitcher. These 
plants are commonly more abundant in the deeper wind-sweeps 
than elsewhere, probably because the sand is moister and more 
stable in the sweeps than at other places. Fig. 7 shows a very 
characteristic wind-sweep with its vegetation composed of the 
bugseed and other short-lived plants. 
Although the summer winds are much less severe than those 
of winter, the effects on the vegetation of the wind see 
often conspicuous. Artemisia and Corispermum plants 
quently have the sand blown away from their roots and — 
thus obliged to lean over on the sand. The stems become Re 
twisted and the whole plant is shorter and more eon a 
when developed in more protected habitats. esc si 
nials that may germinate in such places rarely live overt aa 
ter. The vegetation develops anew each year and . _ 
toward capture are taken. The conditions on the lee 5 ya 
the complex are much like those on the main advancing sins 
Of course all of the vegetation is subsequent. The ae “ae 
are, perhaps, more severe because more uncertain. ie com 
covered with Ammophila are common on the Glen Ha Aare 
plex. Permanent capture may sometimes result on ee ig? 
but it is much rarer than at the slowly advancing edg 
complex. 
