Seasons in Southern Arizona. 245 



Trees and shrubs. The greater number of trees of the 

 region come into bloom during this period. Of these, Park- 

 in soiiia micro pJiylla (palo verde) and P. torreyana are true 

 desert trees, having very minute leaf-blades which are cast 

 at any time when the water supply fails, and which use the 

 green layers of the bark instead when the leaves are lacking. 



The winding sandy course of a dry streamway bordered 

 by palo verdes loaded with golden yellow bloom furnishes 

 a view hardly surpassed in beauty by anything furnished by 

 the southwest. The trees are also sufficiently abundant on 

 some slopes to make the dominant note of color. 



Two other pod-forming groups of trees are also active 

 at this time, the acacias and the mesquites. Of Acacia there 

 are two species, one with white and the other with yellow 

 flowers, which are sweet-scented and are borne in globular 

 cluster on the small trees. Mesquite attains its greatest 

 growth on the alluvial bottom lands, and it is capable of 

 sending long roots to a great depth in search of water. The 

 delicate green of its leaves is an especial feature. In April 

 and May small racemes of whitish flowers are followed by 

 the pods and bean-like seeds, which are such an important 

 feature in the life of many animals and of the Indians. 



Poplars are invariable indicators of the presence of 

 underground water and they mark the streamways wherever 

 an underflow yields a supply during the dry season. Some of 

 the trees along the upper courses of the Santa Cruz and along 

 the Rillito attain enormous proportions of trunk and spread 

 of crown. Singularly enough the same species climbs up a 

 half mile in elevation to follow the water courses into the 

 mountains. A similar extreme range seems to be attributable 

 to the walnut. The walnut of the Tucson region {Juglans 

 major) is frequent for the most part in valleys at 3000 and 

 4000 feet but the tree which grows in some abundance at 

 various places in the Santa Catalina Mts. at elevations of 

 8000 feet seems to be identical with it, thus giving this 

 species a range of a vertical mile from a sub-tropical to a 



