Western Sierra Madre Region. 643 
Cupressus Arizonica Greene. | Pinus latifolia. Sarg. (= P. Mayriana 
Juniperus pachyphloea Torr. > chihuahuana Engelm. [Sudw.). 
» occidentalis Hookvar. mono- » _ strobiformis Engelm. 
sperma Engelm. | Pseudotsuga Douglasii Carr (= P.taxi- 
> virginiana L. folia Poir.). 
Pinus reflexa Engelm. Abies concolor Lindl. & Gord. 
»  cembroides Zucc. Yucca elata Engelm. (= Y. radiosa 
» arizonica Engelm. Engelm.). 
» ponderosa Laws. »  macrocarpa Cav. 
In the Santa Rita Mts. occur such herbs as Phacelia crennlata, Castilleia integra, Rumex 
hymenosepalus with such woody plants as Cereus phoeniceus, Fendlera rupicola while the des- 
cending slopes are covered with Astragalus mollissimus, A. missouriensis, A, humistratus, 
. cobrensis, A. Shortianus and A. Nuttallianus. The canyons of the Huachuca Mountains have 
‚among other plants, the following: Ceanothus integerrimus, Vitis arizonica, Robinia neomexicana, 
Stevia Plummerae, S. serrata, Erigeron divergens (under bushes), Cacalia decomposita, Euphorbia 
montana, Guilleminea densa (= G. illecebroides), Lilium Parryi, while on the canyon sides grow 
Cereus caespitosus, Opuntia arborescens, Baccharis pteronioides, etc.?). > 
3. Chihuahuan Desert Region. 
This phytogeographic region is coincident with the central Mexican 
tableland which stretches at a nearly uniform elevation of 7,500 feet for a 
distance of about a thousand miles, north and south. But the uniformity of 
this plain formed by the progressive and long-continued accumulation of detrital 
material is broken by barrancas, or enormous ravines, sinking hundreds, perhaps 
even a thousand feet into the ground and measuring several miles across. The 
climatic conditions, lack of rainfall, etc. render this plain an arid waste, or 
desert, where xerophytic, succulent plants (see Caciaceae Fig. 30) 
form the marked feature of the vegetation. Three types of succulent plants 
form the bulk of the xerophytic vegetation of the Chihuahuan desert region, 
viz., the cactus type, the yucca type and the agave type. 
The country bordering the Rio Grande in Chihuahua and Texas is nearly 
destitute of trees, except in certain localities, as on the bottom lands of the 
Rio Grande and Rio Concho. The lowlands are thickly set with Prosopis 
glandulosa and along the arroyos grow Populus monilıfera, or P. angustifolta, 
Celtis occidentalis, Fuglans rupestris, Ungnadia speciosa, Guatacum Coulteri, 
Larrea Mexicana and Fouquiera splendens’). 
Chaparral Formations. These are best developed in trans-Pecos, u 
and the same type is found in the northern part of the Mexican piateau. 
Compared with the Rio Grande chaparral (later to be discussed), the nun 
and Caesalpinieae form according to BRAY less than ten per ee = 
Species, while Prosopis juliflora becomes a shrubby plant and a grea Kr 
ance of the Zphedra, Croton, Eurotia and Larrea types also no . 
ı) Rose, J. N.; List of Plants: see Bibliography p. 78. 
2) NEWBERRY, J. S: See Bibliography p. 77- 
ES. 
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