40 



RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



to rubber culture. The few samples thus far analyzed furnish a very 

 insufficient basis for a judgment as to the amount of rubber that it may 

 be expected to yield. The stems grow in clumps to a height of 2 to 

 3 feet and are densely clothed with broadly oblong, hoary-tomentose 

 leaves in whorls of 3 or 4 at each node. The species is an inhabitant 

 of poor soils, often growing in places too stony or dry for other than 

 a low growth of herbaceous plants, and is limited in its distribution to 

 California, from the upper end of the Sacramento Valley south to 

 San Diego County, growing in the hottest valleys and on exposed 

 foothill slopes, but not upon the desert. Although often crowded 

 out into poor soils, it responds readily to better treatment, as is evident 

 by the exceptionally vigorous growth made when it is occasionally 

 permitted to develop in young orchards or cultivated fields. A plant 

 of this sort (915), gathered at Atascadero, in the south Coast Ranges, 

 October 15, 1919, was found to contain 2.2 per cent of rubber in the 

 leaves and 0.7 per cent in the stems. The parts analyzed were from 

 second growth, the original spring growth having been cut earlier 

 in the season. The leaves of a plant (939) gathered at Auburn, in the 

 Sierra Nevada foothills, on June 19, 1920, yielded 1.3 per cent of 

 rubber. Another sample (944) from Coming, in the northern part of 

 the Sacramento Vajley, gathered July 12, 1920, carried 2.4 per cent 

 in its leaves and 0.5 per cent in the stems. 



Table 11. — Chemical analyses of Asclepiodora decumbens. 



No. 



339 

 372 



882 

 983 



985 



Place of collection. 



Trinidad, Colo 



Near Manitou, Colo 



Pike's Peak, Colo 



Near Salt Lake City, Utah 



.do. 



Date of 

 collection, 



Aug. 15 

 July 14 

 Aug. 31 

 Sept. 1 



.do. 



Part of plant 

 analyzed. 



Leaves 

 Whole . 

 Whole. 

 Leaves 

 Stems . 

 Leaves 

 Stems . 



Acetone 

 extract. 



p. ct. 

 9.5 

 9.2 

 8.0 

 7.7 

 9.1 

 8.5 

 10.0 



Rubber 



(benzene 



extract). 



P 



ct. 

 1.2 

 1.3 

 0.8 

 1.7 

 0.4 

 1.0 

 0.5 



Asclepiodora decumbens. — The stems of this milkweed are 1 to 2 

 feet long and spreading or decumbent. They grow in clumps from 

 deep, perennial roots. The leaves are alternate, lanceolate, 0.25 to 

 nearly 1 inch wide, and nearly glabrous. The plants resemble some 

 of the species of Asclepias in general appearance and could probably 

 be handled much like A. latifolia or A. calif ornica, but they differ 

 from all of the true milkweeds in the entirely alternate leaves and in 

 the flowers, the corona-hoods of which are prominently crested within 

 instead of being provided with horns. In the bast fibers and the down 

 on the seeds they are quite similar to Asclepias. The distribution is 

 from Kansas west to Utah and south to Texas, Arizona, and Mexico, 



