MISCELLANEOUS SPECIES. 



39 



The quality of the rubber from Apocynum is said by Fox to be much 

 superior to milkweed rubber, as will be noted on p. 54. 



TABLE 10. Chemical analyses of Apocynum cannabinum and A. androsccmifolium. 



1 A. androssemifolium. 



2 A. cannabinum . 



VI. MISCELLANEOUS SPECIES. 



In addition to the 10 species reported upon in the preceding pages 

 there are 6 which, while not of such promise as these, yet will need to be 

 considered in connection with any study of the native rubber plants 

 of North America. In all cases the number of samples analyzed is 

 so small that further examinations should be made. Quite possibly 

 some of the species placed in this second list will be found on further 

 study to excel those of the preceding group. All but the last two are 

 members of the Asclepiadaceae, or milkweed family. 



Acerates auriculata. This is a green and nearly glabrous plant with 

 the aspect of an Asdepias. The stems are 3 feet or less high and the 

 leaves are narrowly linear or filiform, so that the amount of rubber- 

 carrying herbage that could be produced on a given area of land would 

 not be so great as that from the true milkweeds. The species ranges 

 from Nebraska and Colorado to western Texas and New Mexico, and 

 grows in dry, stony, or sandy soil. A single collection (389) from 

 Denver, Colorado, yielded on analysis 2.9 per cent of rubber from 

 the leaves and 0.5 per cent from the stems. Another species, the 

 green milkweed (A. viridiflora) , with much more copious foliage, is 

 reported upon in table 12. 



Asclepias eriocarpa. The robust habit, leafiness, and ecologic re- 

 quirements of this species are such as to render it especially suited 



