178 



hei'baceous flora resembles that of the most mesophytic of our 

 upland woods. 



Some Adaptations of the Plants to the Environment. 



The plants of the sand region are nearly all xerophytes, 

 and as such show many xerophytic adaptations for the reduc- 

 tion of transpiration. Some of the more important of these 

 are given below, and illustrative plants mentioned. 



1. Rfdudloti of flic Leaf Siirfdcc — Opiiufin luiiin'fiisa. the 

 cactus or prickly pear so common throughout the region, is the 

 best example. The leaves are no longer functional, and the 

 green succulent stem is divided into fiat obovate joints which 

 transpire very slowly. 



2. Thick or Si(crn/f'iit Lcarcs. — Tultiiiuii nii/o.spei'iinnii has a 

 basal cluster of cylindrical succulent leaves one to two inches 

 long. Plii/so.stegi(/ riiyiin(ni(i when growing on the sand prairies 

 has blunt-toothed leaves, slightly folded along the midrib, and 

 greatly thickened. The difference l)etween this leathery-leaved 

 xerophytic form and the thin-leaved mesophyte abundant 

 along ditches and sloughs elsewhere in the state, is very strik- 

 ing. 



3. Xafj'oir of Liiicdf Leaves. — A reduction of the transpir- 

 ing surface by linear leaves occurs in many species, among 

 which are Polijyoiiuni fe)ii(e,Poli/f/ii/(i verticiUata. Pffalo.sfeinoH caii- 

 (lidiis and P. ptirpiircKs, Pli/o.r bifida, and lo/iarfis Jinariifolius. 



4. A Protcrfire CorcriiKj of Hairs or Scales. — This is one of 

 the commonest adaptations for preventing excessive transpira- 

 tion, and is found on a great many of the species. Frodichia 

 raiiqjcsfris is softly graj'-hairy througliout; Ainorplia caiiesceiis, 

 ('raced rirf/iiiiana, and CJiri/sopsis lyni/jxir'ni) are densely hairy, 

 giving them a gray appearance; and Crofoii (jlaiidalosus has a 

 thin covering of stellate hairs. The linear leaves of Crofonopsis 

 linearis Rve silvery with stellate hairs, and in Lesijucrella spafJni- 

 lata there is a l)asal rosette of spatulate leaves silvery with stel- 

 late pubescence. The glandular hairs with which the stem of 

 Cristatella Janiesii is covered, hold the sand blown against it 

 by the wind, so that the plants become encased in a veritable 



