96 



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 



T»>>';i;'V,' Transition grass land to deciduous 

 ■■■"'■•'"■'■' forest 



- ^ Deciduous forest 



■ Western xerophytic fore-^t, dwarf 

 junipers, etc. 



"tJlC^ Transition desert to grass land 



Viv'/U Grass land 



^ Transition to evergreen forest 



4 A Evergreen forest. No attempt is made 

 ^ to distinguish northern and southern 



\^ 1^ Swamp 



Fig. 58. — jNIap 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- 



