CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 



235 



physiological responses all were tried. The most successfully ap- 

 plicable value he found 156 was one that combined a physiological 

 temperature index, precipitation, and evaporation. Actually this 

 was a refinement of the precipitation : evaporation ratio proposed 

 earlier, 255 but it is scarcely more useful. These and other studies 

 serve to emphasize the complexity of plant-environmental rela- 



1 



m TUNDRA 



ED BOREAL FOREST 



E%1 HEMLOCK-HARDWOOD F. 



ES3 DECIDUOUS FOREST 



E-7H3 S.E.EVERGREEN FOREST 



Fg~\ GRASSLANDS 



r?rl DESERT CRASS AND SCRUB 



r^il DESERT 



V77ZK COASTAL FOREST 



rrrrm rocky mt. forest 



E^ WET AND DRY TROPICAL F. 



FlG. 111. General ranges of the principal vegetation types of North Amer- 

 ica.— By permission jrom Transeau, et al (1940)~ 5: Harper and Brothers, pub- 

 lishers. 



