14 - BULLETIN 745, TJ. S. DEPARTMENT OF AGRICULTURE. 



mon species of the yucca group of drought-resistant plants in the 

 Southwest. It is one of the common plants on the dry plains and 

 mesas from western Texas throughout southern New Mexico to 

 southern Arizona, and extends into Mexico. It occurs commonly on 

 the sandy soil which is the favorite habitat of the black grama grass 

 (Bouteloua. eriopoda), on which it reaches its maximum size in 

 southern New Mexico. The stand on such areas may vary from a 

 few to 300 plants per acre. Soapweed grows to some extent also on 

 the clay flats and gravelly slopes adjacent to the sandy soil but does 

 not reach its maximum stand on such areas. It is found only occa- 

 sionally on the sandhill areas, probably because the unstable soil 

 conditions make it difficult for the soapweed to establish itself there. 

 Wherever it has become established on the sandhill areas, however, 

 there is often produced a heavy stand. Further study is necessary, 

 therefore, to determine the factors limiting distribution. 



As is indicated by its occurrence in different habitats, soapweed 

 will grow in sandy, gravelly, or heavy clay soil. It is not exacting 

 in its moisture requirements. It commonly reaches 5 or 6 feet in 

 height and sometimes grows as high as 30 feet on the plains where 

 the annual rainfall is less than 9 inches. On the other hand, it has 

 been found growing on the embankments of storage tanks at stock- 

 watering places where the soil is very moist, and the growth seemed to 

 be little or no different from that on drier areas. 



Soapweed commonly reaches a height of from 4 to 6 feet, with a 

 stem diameter varying from 3 to 6 inches. Occasionally, specimens 

 reach a height as great as 30. feet and a diameter slightly greater than 

 6 inches. Yu'cca elata is different from most palm or grasslike plants 

 in thaf the stem undergoes diameter enlargement after elongation, or 

 height growth, has begun. This permits additional increase in 

 volume and value of the plant aside from height growth, which is 

 very slow after the plant reaches from 4 to 6 feet. 



As in many other drought-resistant plants, growth in soapweed 

 is very slow. At best the plant requires several years to reach the 

 average height of from 4 to 6- feet. Judging from the growth of 

 two-year-old plants, it will take about 10. years for new plants to 

 reach a height of 36 inches or over, which now appears necessary 



stouter than those of Y. elata.), and, moreover, its fruit is pulpy, the flesh often being 

 nearly J inch thick. 



Another Southwestern yucca that usually has a treelike form is Schott's yucca (Yucca 

 8chotti Engelm.), of southern Arizona and Sonora. Its leaves are flat except toward 

 their concave tips, smooth, light yellow to bluish green, 16 inches to 3 feet long, 1 to \\ 

 inches wide, the thickened, untoothed margins finally breaking into short brittle threads. 

 Other distinguishing characters are the hairy-woolly, inflorescence and the late (October- 

 November) ripening fruit, with its thin, sweet, pulpy coating. 



Yiu-cu macrocarpa (Torr. ) Coville, ranging from western Texas to southern California, 

 is distinguished by its long (up to about 3 feet), spiny, concave, yellow-green leaves, very 

 early flowers (March and April), long-stalked stigmas, and oblong, blackish, fleshy, sweet, 

 and edible fruits, 3 to 4 inches long, terminating in an abrupt point or terminal appendage. 



