24 



The Plant World. 



culent forms of the dry fore-summer, plants of the humid mid- 

 summer, summer perennials and annuals, and species belonging 

 to the dry after-summer. A section is devoted to temperatures 

 of plants in the desert, and other divisions to the water and soil 

 relations of desert plants, in which are embodied also the results 

 of recent studies of the root systems of various species. Of 

 special interest are the concluding chapters on conditions con- 

 tributory to deserts, their formation and extent and the influence 

 of the desert on life. A geological sketch of the region of Tucson 

 is contributed by Professor Wm. P. Blake, Territorial Geologist 

 of Arizona. 



The numerous plates, some of which had appeared in Publi- 

 cation No. 6 of the Carnegie Institution (the forerunner of the 

 present work) serve fully the purpose of illustration, but it is 

 to be regretted that notwithstanding the good quality of the 

 paper they fail to do justice to the original photographs. 



All in all this paper constitutes the most available source 

 of authentic information regarding the topography and plant 

 life of the great desert region of the southwestern United States 

 and Mexico, a region that economically as well as from the scien- 

 tific standpoint is assuming great importance at the present time. 



