20 RANGE IISrVESTIGATIONS IN ARIZONA. 



gentle, grassy slopes between the arroyos in this vicinity reveals. a 

 very scattering growth of mesqviite {Prosojj/s vehif/ina), which is in 

 the form of twigs 2 to 3 feet high, with an occasional larger shrnl) 

 in some of the more favorable localities. Without more critical data 

 regarding the previous history of the region than it is possible to 

 secure at the present time, one can not tell wliether this growth indi- 

 cates that this shrub is spreading or not. The present condition 

 rather suggests this possibility. It would not be at all surprising, for 

 there appears to be abundant evidence that such is the case under the 

 influence of stock grazing in portions of Texas, where a closely related 

 mesquite grows in abundance. 



By far the most important shrub is the mesquite, which, like the 

 majority of the other shrubs, is especially at home from the line LI, 

 figure 1, northward and along the arroyos in the southern half of the 

 inclosure. In many localities in the southern half cat-claw [Acacia 

 (iri'(i(/i/) is nearly as abundant as the mesquite at the present time. 

 This, however, is better protected than the mesquite, and the wood 

 choppers have generally avoided it on this account. The other smaller 

 species of acacia (^1. constrictd) is less alnindant, but is also confined 

 to the arroyos. The blue palo verde [Parhinsonia torreyana), which 

 rivals the mesquite in size, grows in similar localities. The desert 

 willow ( Chilopsis Unearix)^ cottonwood [Pojndwi freinontii)^ hackberi-y 

 {Celtis reticulaia), soapl)erry (Sapitidus marginatiis), and walnut 

 {Juglanfi callfornica) grow sparingly in some of the upper canyons. 

 A large part of the northwestern portion of the field is badly infested 

 with Imcoina cor<m()]_)tf<>lia. The line LI, figure 1, passes through a 

 very conspicuous growth of large bunches of Zizlplms lycioides, which 

 is of as little value as the creosote bush {f-ovillea tridentata), which 

 occupies some of the southeastern portion of the field. The greater 

 part of the latter was avoided, however, in the final fencing, a very 

 large area being found immediately north of the eastern portion of 

 the inclosure. The upper edges of it arc included in the northeastern 

 portion of the field and in places along the northern portion of the 

 McCleary road to Tucson. The line LI also represents the most pro- 

 fuse growth of the Cactacea?, the main species of which are prickly- 

 pear {Opimtla engdmanni)^ cholla {Ojnoitia fidgida)^ and Opuntia 

 sjnnmior. These, together with the sewarah {Cerexis giganteus)^ are 

 the most conspicuous of the cacti within the inclosure. The biznaga 

 {Echinocactus wislizeni) occurs in scattering individuals over the 

 entire tract. 



Of the other cacti little need be said. Opuntia arbnscula grows 

 scatteringly on the northern portion, while Cerens fendleriana and 

 C. greggii are occasionally found in the same region. On the rocky 

 banks and higher bluffs are numerous other inconspicuous species, 

 such as Mammillaria grahami., M. arizonica^ Gereus rigidissimus^ and 



