9 6 



A NATURALIST IN THE GREAT LAKES REGION 



At the other extreme are the xerophytes, plants growing where 

 the evaporation tends greatly to exceed the water supply. The 

 open dunes give an excellent illustration of such conditions. 



Unmarked (lower, left) desert 



-^~ Semidesert 



Western xerophytic forent, dwarf 

 junipers, etc. 



~*ZZ~ Transition desert to grass land 



V<y.'V/;, : Transition grass land to deciduous 

 : - ''''<' forest 



J* Deciduous forest 



tyffffif, Transition to evergreen forest 



A * Evergreen forest. No attempt is made 

 * + to distinguish northern and southern 



vX'$ Grass land ^ ^> Swamp 



FIG. 58. Map of vegetation areas in Eastern United States. After Shreve 



The great majority of plants grow where there is neither excess 

 nor dearth of water and are known as mesophytes. This ratio 

 of evaporation to rainfall is a very important factor in deter- 



