134 The Plant World, 



both ecologically and floristically related to the continental 

 deserts they are nevertheless not to be looked upon as climatic 

 deserts, but as edaphic areas of desert in a savanna region, 

 belonging in the same category as coastal dunes. A relatively 

 high and constant humidity gives the atmosphere an evaporating 

 power which is m.ore nearly that of humid coastal regions in the 

 sub-tropical United States than it is that of the inland desert 

 region of Arizona or even that of the semi-desert coast of 

 Southern California. 



A COMPARISON BETWEEN TWO MOUNTAIN SIDES. 



By J. C. Blumer. 



During a reconnaissance of the Rincon Mountains of south- 

 ern Arizona in the summer and autumn of 1909, it early became 

 apparent that a considerable difference in the plant covering 

 existed between the two sides of the range. A similar difference 

 has been detected in the Baboquivari and the Santa Catalina 

 mountains. The RinCons are covered with a forest which at 

 this altitude of 7,000-8,000 feet (2,100-2,400 m.) is composed in 

 the main of Pinus arizonica and several evergreen oaks, with 

 ceanothus underbrush and perennial and annual herbs and 

 grasses, the perennials being dominant. To state briefly some 

 of the points in categorical form, it was found that the east side 

 differed from, the west side in the following particulars : 



1. The timberline, bv which tenn the loiver limit of ever- 

 green tree growth is here known, is found at a lower altitude, 

 and the different zones of vegetation range lower. 



2. The trees and tall shrubs are larger, taller, straighter, 

 m.ore thrifty and cleaner of limb. 



3. A number of additional species of trees and shrubs 

 are present occasionally on open slopes, on the west side rarely 

 or never seen except in gulches. Among these are Arbutus 

 arizonica, Vitis arizonica, Rhamnuscalifornica, Saynhucus glauca, 

 Rohinia neo-mexicana, Parthenocissus quinquejolius, Rhus glabra, 

 Primus salici folia acuti folia. 



4. An aspen grove is present on a somewhat open slope, 

 at an elevation of only 7,400 feet (2,250 m.), under which twines 

 not a little Humulus lupulus,and whose floor is covered with 



I 



