94 THE PLANT WORLD 



aspect of the vegetation is highly xerophytic although of 

 some abundance. An analysis of the flora, however, shows 

 that a large proportion of it, as in all western American 

 deserts, is made up of annuals and perennials which are 

 active only during the periods of maximum precipitation in 

 summer and winter. These forms do not exhibit any struc- 

 tures which distinguish them from mesophytic species of 

 moister regions, but they show peculiar rhythms and 

 dormancies. The seeds of many of the winter annuals will 

 germinate only in the low temperatures of the winter months, 

 lying wholly inactive during the summer rains, while the 

 summer annuals are equally unaffected by the moisture and 

 stimulus of change of the cooler months. As a result of the 

 arrangements in question, the vegetation shows an intricate 

 interlocking of temperate and sub-tropical forms with, of 

 course, a very large number of endemic species of both 

 classes. Legumes are abundant and are represented by a 

 great number of species. Most remarkable of all however, 

 are the cacti, comprising a group of forms of comparativ^ely 

 modern origin, and including hundreds of species, some of 

 which are extremely restricted in distribution. 



The area in question is of increased interest since its in- 

 habitants include the Papago Indians, a desert race that was 

 differentiated from the Piman stock, and these bean-growing 

 farmers ha\ e li\ed here in aeijustment to the arid conditions 

 for ten or twelve centuries and are at present but little dis- 

 turbed by the civilization of the white race, although the 

 most meaningless international boundary in the world cuts 

 diagonally across their domain, which was designateci as 

 Papagueria by the earlier Spanish e\ph)rers. Thev still 

 dominate the country as a whole, and the relations of their 

 activity to the climate and to the other living forms are as 

 interesting biologically as anything to be found in any un- 

 disturbed area. 



The work of the naturalists of the boundary survey 

 Commission after the Gadsden purchase, made an unmeaning 



