178 



herbaceous 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. Redaction of the Leaf Surface, — Opaatia humifusa, 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 flat obovate joints which 

 transpire very slowly. 



2. TJiiek or Succulent Leaves. — Talinum najosperiaaia has a 

 basal cluster of cylindrical succulent leaves one to two inches 

 long. Physostegia virginiana when growing on the sand prairies 

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

 greatly thickened. The difference between this leathery-leaved 

 xerophytic form and the thin-leaved mesophyte abundant 

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

 ing. 



3. Narrow or Linear Leaves. — A reduction of the transpir- 

 ing surface by linear leaves occurs in many species, among 

 which are Polygonum tenue, Poly gala verticillata, Petalostemon Can- 

 didas and P. purpureas, Phlox bifida, and Ionactis linariifolius. 



4. A Protective Covering 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. Froelichia 

 campestris is softly gray-hairy throughout; Aaiorpha canescens, 

 Cracca virginiana, and Chrysopsis camporum are densely hairy, 

 giving them a gray appearance; and Croton glandulosus has a 

 thin covering of stellate hairs. The linear leaves of Crotonopsis 

 /incaris&re silvery with stellate hairs, and in Lesquerella spathu- 

 lata there is a basal rosette of spatulate leaves silvery with stel- 

 late pubescence. The glandular hairs with which the stem of 

 Gristatella Jamesii is covered, hold the sand blown against it 

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



