1899] DUNE FLORAS OF LAKE MICHIGAN 201 
most pronounced xerophytic adaptations to be found in this lati- 
tude, These xerophytic structures will be discussed in the sec- 
ond part of this paper. At this point it is necessary only to state 
that in the main they are to guard against excessive transpira- 
tion, such as is induced by the unusual exposure to wind, heat, 
and cold. Ina certain measure one might attribute these xero- 
phytic adaptations to an insufficient amount of water in the soil, 
since, were they absent, the soil water would soon be used up. | 
But it is much more important to discriminate, as ecologists are 
tow coming to do, between conditions in the soil and those in 
the air. A plant may have its roots in the water and yet be 
“posed to a xerophytic air; in that case the aerial organs will 
. set with xerophytic adaptations, as is the bulrush. 
Schimper, in his recent plant geography, goes still farther and 
a ates Plants hy grophytic at one season and xerophytic at 
a. Perhaps the ultimate definition of a xerophyte will be 
4 plant that is endeavoring to reduce its transpiration. : 
Directly or indirectly, the wind is the factor primarily 
cc. for the Scarcity of vegetation on the dune-complex. 
aad Joa as been stated, the wind dries up the soil and 
of the w;  aeplas Incidentally, too, the mechanical action 
"eletotion a3 con with the sand-blast is destructive to 
Dircves : The cardinal destructive influence of the wind, 
Plants, . In its power to cover and uncover the dune 
adapted ih peets have been referred to as peculiarly well 
4 small herb aie Corispermum and Populus. The former is 
to any erea « 2 unable 1 endure either covets or uncovering 
duration and . This plant, however, is an annual of ae 
Wind activity, *S not exist during the periods of the greate 
Mistiod Body which has been shown to be best fitted e 
tt first to oo of dune conditions, might be se ne 
PoWers of endu . abundance there. It has almost maori 
“Vered to the a in all conditions of exposure ; it may : 
4 depth of — per branches, or may have its roots uncovere 
© or three meters, and yet flourish, Its failure 
