184 J. C. BLUMER 



land — is the palo verde, Parkinsonia microphylla. It is usually 

 by far the most abundant of the low and bushy desert trees, dotting 

 the surface as single individuals in orchard-like disposition, forming 

 the real body of the forest. Its olive green appearance undergoes 

 no perceptible change between winter and summer, for although 

 it has its seasons of leafing and leaf-fall, regulated primarily by the 

 seasons of rainfall, the leaves are so minute that a novice needs 

 to handle a branch before he can convince himself of their presence 

 or absence. Along the larger washes Prosopis velutina, Acacia 

 greggii, and an occasional Cercidium torreyanum are present, while 

 areas of Olneya tesota, the ironwood, also appear. This is the 

 largest and handsomest tree of the desert, reaching occasionally 

 a height of 25 or 30 feet and a trunk diameter of 12 inches, and, 

 unlike the palo verde, producing a very hard and heavy wood. 

 All these species, — aside from the arborescent cacti the only trees, 

 —belong to the Leguminosae, representing each of its three sub- 

 families. The mining companies have large amounts of wood 

 cut and hauled for their own use by the Indians at the extremely 

 low cost of $1 to $1.50 per cord. 



A striking feature of the landscape, overtopping the bush forest, 

 is the giant cactus or sahuaro, Carnegiea gigantea. In the vicinity 

 of Tucson it is of more localized distribution, seeking its most 

 favorable situations on rocky hills and mountain sides. Here, 

 in the midst of the desert, it raises its giant columns on every 

 hand, plains and hills alike, except that it is usually scarce on the 

 finer soils and the shadier sides of the hills. As elsewhere, it 

 is especially strong on rocky southerly aspects, with dark-colored 

 rock and soil, on the mountain sides, and on rough, eroded topog- 

 raphy, and coarse, gravelly or rocky soils of the detrital plains. 



Nearest of kin to the sahuaro, in this region, is the pitahaya 

 or organ cactus, Lemaireocereus thurberi. The first specimens of 

 this plant were seen on a rocky south slope in the Cababi hills. 

 Later perhaps a dozen more were seen in similar habitats in the 

 same hills, and it was reported to the writer on trustworthy 

 authority from the south end of the Comobabi mountains and the 

 Quijotoa range. In the latter it was found by the MacDougal 

 expedition of 1907. It was not found by the writer in skirting 



