34 



RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



amount of rubber present. The somewhat high yield of 5.2 per cent 

 in the leaves of one collection seems to justify the hope, however, that 

 further examinations would show that it would average at least as 

 high as in ^. mexicana. These two species are so closely similar in 

 their botanical characters that the extent of variation found in mexi- 

 cana may be reasonably predicted for galioides. A cross between the 

 two, using the individuals with the highest rubber-content in each case, 

 might bring results of interest. 



ASCLEPIAS BRACHYSTEPHANA. 



Description. — Plant a comparatively slender leafy herb, 1 to 2 feet 

 high; roots thick and woody, producing clusters of stems, the clusters 

 perhaps connected by deep horizontal cross-roots; stems usually 

 branched near the base, but otherwise mostly simple and straight, 

 erect, very smooth, and without hairs; leaves numerous to the top, 

 commonly 15 to 30 on each shoot, all opposite, narrowly lanceolate, 

 2 to 5 inches long, 0.25 to 0.5 inch wide, rather thin, smooth, veiny, 

 not hairy; flowers pink or dull purple, small, appearing from April 

 to August, or even September after summer rains, in small, short- 

 stalked clusters among the upper leaves; pods on sharply deflected 

 stalks, erect, narrowly ovoid, long-pointed, 1.5 to 3 inches long, about 

 0.75 inch thick when mature, covered when young with a fine gray 

 scurfy tomentum, but smooth and nearly glabrous in age, maturing 

 from middle July to October. 



References.— Grav, Syn. FL, 21; 94, 1878. Britton and Brown, 111. Fl., ed. 2:31, fig. 

 3402, 1913. 



Distribution and ecology. — This species is most abundant in New 

 Mexico, but ranges west almost throughout Arizona, where it is much 

 less common, and southeast into western Texas. It occurs also in 

 northern Mexico. Specific locahties include the forestry experiment 

 station and the Turney pasture, both near Las Cruces, New Mexico. 

 The plants have rather well developed xerophytic characters and grow 

 on dry mesas and foothill slopes. They are especially common on 

 overgrazed or otherwise disturbed areas. 



