CHAPTER II. 



THE ENVIRONMENT. 



GEOGRAPHICAL DISTRIBUTION. 



The northern limit of distribution of the guayule is in the southwest- 

 ern part of Texas, where it occurs in Presidio, Brewster, and Pecos (near 

 Langtry) Counties. This area is continuous with its area of distribu- 

 tion in Mexico, throughout which it occurs with greater or less frequency. 

 The periphery of this area runs approximately as follows: from the west- 

 ern extremity of Presidio County in Texas, the western boundary will run 

 somewhat west of south till it reaches the northern boundary of Du- 

 rango, near Santa Barbara, Chihuahua. 1 From this point the limit turns 

 approximately toward the southeast, running parallel with the Mexican 

 Central Railway at a distance of about ioo kilometers (Endlich, 1905). 

 Beyond the state of Durango the boundary turns still farther to the east, 

 curving northward again not far from the city of San Luis Potosi. 2 The 

 101st meridian marks roughly the eastern boundary, lying somewhat west 

 of it till beyond Saltillo, where the boundary then curves slightly west of 

 north, reaching the eastern limit in Texas at about Langtry. The north- 

 ern limit is marked approximately by Fort Stockton. 



The guayule is thus seen to be peculiar to the Chihuahuan desert. 

 The belief which has sometimes been entertained that it occurs in western 

 Sonora, southern Arizona, and New Mexico seems not to be well founded, 

 and the area within which it is found is confined to the northern portion of 

 the central plateau, embracing an area of approximately 130,000 square 

 miles, or 290,000 square kilometers. Of this area, it will be understood 

 that only a small proportion will be found to carry guayule, and a rough 

 estimate of 10 per cent would certainly not be too low. Endlich's (1905) 

 estimate, 75,000 square kilometers, is probably as nearly correct as we 

 may make it. It may here be remarked that the very great irregularity 

 of distribution makes it very difficult indeed to make anything approach- 

 ing an accurate estimate of the amount of guayule as to acreage alone, 

 aside from the question of density, so that any figures which may be given 

 are subject to correction. 



ALTITUDINAL DISTRIBUTION. 



The whole region in question is, as already said, embraced within 

 the northern part of the central plateau (mesa central) of Mexico and 

 the adjacent area within which guayule is found in Texas. This area 

 has an altitude varying from 2,000 to 10,000 feet above sea-level. The 



1 Mr. W. H. Stayton reports seeing a small amount of guayule in the Sierra 

 Madre east of Sahuaripa, Sonora. The amount on the eastern slope was somewhat 

 greater than on the western. It is now believed to occur sparingly in eastern Sonora. 



2 I am informed that Pringle found guayule near Pachuca, Hidalgo, which is 

 probably its southernmost limit. 



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