98 



A NATURALIST IN THE GREAT LAKES REGION 



Many marked structural peculiarities and adaptive life- 

 habits go along with the ability of the plant to endure drought 

 or excessive moisture. Since the loss of water goes on largely 

 through the leaves, the leaf surface of the xerophyte is often 

 reduced in proportion to its volume by the leaf being needle 

 shaped rather than fiat and thin. The leaf surface may be 

 covered with hairs, and so evaporation becomes reduced, or the 



Fig. 6o. — The cactus, Opuntia Rafinesquii, in fruit in the dunes 



surface may be covered with impervious wax; such a weed as 

 the mullein, growing in open w^aste territory, is a familiar example 

 of the former, and the glossy-leaved plants of the ground 

 stratum in the pine dunes — like the wintergreen, shinleaf, and 

 prince's pine — are examples of the latter, as is also the very 

 common field milkweed. The oak leaf and that of the cotton- 

 wood are both thicker and glossier than the leaf of the hard 

 maple or beech that grows in the mesophytic conditions of the 

 climax forest. The leaf stem or underground portions of the 



