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NATURALIST'S GUIDE TO THE AMERICAS 



forms of plants' ' (Bray ) . This embraces 

 the cactus-yucca-agave types. 



2. The absence of storage (succulent) 

 tissue, and the assumption of a dwarfed 

 condition as a defense against the ex- 

 treme arid environment. 



The animal life of the region is replete 

 with forms typical of the desert, and 

 there are many forms which are closely 

 confined within the limits of the area. 

 Among the reptiles we find the Texas 

 holbrookia (Holbrookia texana) as a 

 very typical desert lizard, its range 

 extending only into the Pecos arm of 

 the mesquite desert. The horned toad 

 (P. cornutum) is abundant in the arid 

 regions, but this species is at the present 

 time showing marked tendencies to 

 extend its distribution northward, 

 exhibiting a wide range of adaptability. 

 In the very arid regions the whip-tailed 

 lizard (Cnemidophorus t. tessellatus) is 

 characteristic and abundant. Among 

 the mammals, the gray mule deer (Odo- 

 coileus hemionus canus) is closely con- 

 fined to the area, and the black-tailed 

 deer is common. The Texas antelope 

 squirrel (Ammosperimophilus interpres) 

 shows an interesting distribution, being 

 typical of the succulent desert; the east- 

 ern limit of the region marks the limit 

 of the squirrel, and the species does not 

 encroach at all upon the extensions of 

 the mesquite desert. It is confined to 

 the Rio Grande valley and is barred to 

 the eastward by the Pecos. The Pecos 

 River muskrat (Ondatra zibethica ripen- 

 sis} is found in the local extensions of 

 the mesquite of the semi-desert, while 

 the broad-tailed beaver (Castor canaden- 

 sis frondator] is found, though not com- 

 monly, from the Devils river and the 

 Pecos down the Rio Grande as far as 

 Brownsville. The desert cottontail rab- 

 bit (Sylvilagus audubonii subspp.) is a 

 common animal of the open country, 

 and the range of the species extends 

 northward into the grassland and steppe 

 region, where the species frequently 

 uses the holes of the prairie-dog for its 

 habitation. Among the canyons of the 

 Rio Grande and its tributaries an occa- 

 sional cougar (Felis concolor group) 



is found, and these animals cause serious 

 loss to stock breeders. The "civet cat" 

 (Bassariscus astutus flavus} is very com- 

 mon over most of the region, and is a 

 characteristic form in the area. 



9. Xerophytic coniferous forest 



This region, the country of the juni- 

 pers and the pinion, is best represented 

 in the state by a series of "islands" 

 isolated from one another as the tops of 

 the mountains of the trans-Pecos region. 

 Thus we find in the extension of the semi- 

 desert broken steppe country that 

 injects itself into the heart of the succu- 

 lent desert, three distinct areas of semi- 

 desert coniferous forest, represented 

 by the Guadaloupe, Davis and Chisos 

 mountains. A comparison of the flora 

 of these three regions shows that, while 

 each has a flora characteristic of itself to 

 a certain extent, there are certain forms 

 that are common to all of them. Of 

 these we can list the following: bull 

 pine (Pinus ponder 'osa), mountain sugar 

 maple (Acer grandidentatum), Quercus 

 grisea, Prunus (serotinaf), Rhamnus 

 purshiana and Symphoricarpos (longi- 

 florusf). Comparing in a similar man- 

 ner the mammalian fauna of the three 

 regions, we find again certain species in 

 common, namely : the Mexican wood rat 

 (Neotoma mexicana), the mountain 

 cottontail (Sylvilagus robustus) and the 

 black bear (Ursus americanus) . Among 

 the birds we can list a dove (Columba 

 fasciata), a woodpecker (Melanerpes 

 formicivorus) , a hummingbird (Trochilus 

 alexandri), a vireo (Vireo solitarius), a 

 tanager (Piranga hepatica), and a nut- 

 hatch (Sitta carolinensis nelsoni) . These 

 species are all co-inhabitants of the 

 regions above 6000 ft. at which level the 

 short grasses of the broken steppe give 

 place to the vegetation of the semi- 

 desert forest type. 



Among the other animal forms that 

 must be considered as characteristic of 

 the region we can call attention to the 

 Sonora deer, which ranges in the moun- 

 tains at an elevation of 5000 to 9000ft., 

 usually in close association with the oaks 

 and junipers, as the species depends on 



