The 



Plant World 



J\ Magazine of General Botany 



VOLUME 12 

 NUMBER 8 

 AUG. 190 9 



Causes of Timber-line on Mountains 



By C. H. Shaw 169 



Natural Alternation of Vegetation 



By L. X. Duncan 181 



Books and Current Literature l <SJ 



Notes and Comment 189 



Tucson, Arizona 



Entered as Second C la ss Matter, Dec 17, 1907 , at the Post-Office, Tucson, 

 Arizona, under the Act of Conqress of March 3, 1879. 



