60 KUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



of the opinion that there will be no insurmountable diflficulty in so 

 constructing the rubber machinery as thoroughly to separate the fiber 

 without injuring it. It seems reasonably certain, therefore, that not 

 only could both rubber and fiber be extracted from the same material 

 in a practical way, but that the extraction of the rubber would permit 

 the paper manufacturer to proceed with considerably less expense 

 than if he were to use the plant as it comes from the field. 



In view of the above favorable reports, it is now proposed to collect 

 a half-ton sample of the desert milkweed in order that the rubber may 

 be extracted and the residue turned over to the paper manufacturers 

 for fiu"ther experimentation and report. 



XII. AGRICULTURAL POSSIBILITIES OF ASCLEPIAS AND 



APOCYNUM. 



If natural rubber is ever produced in commercial quantities in the 

 United States, it will be from a plant which will give large yields on 

 cheap land, and one which can be handled almost entirely by ma- 

 chinery. This is assuming that labor and other economic conditions will 

 remain about as they now are. The reason for these requirements is 

 the realization that North American rubbers, unless possessing unique 

 qualities that would especially fit them for special uses, would need to 

 compete in the market with the foreign product. The price of the best 

 imported grades is now down to about 25 cents per pound, and even 

 this will doubtless be lowered with the improvement of plantation 

 methods and when the present voluntary restrictions on output are 

 removed. Another quaUty which it may be necessary for the Ameri- 

 can-grown plant to possess is the abiUty to yield by-products. It 

 seems quite possible, for example, that while the species of plants con- 

 sidered in this report might never be made to produce a suitable retiirn 

 from their rubber alone, yet their cultivation might become a profitable 

 industry in view of the additional returns to be expected from the 

 sale of the pulp after the rubber is extracted. 



Of all the plants here considered, the desert milkweed (Asclepias 

 subulala) apparently comes nearest to fulfiUing the requirements 

 above set forth. It is a perennial that grows rapidly on poor desert 

 lands with a minimum of moisture, is of such a nature as to permit of 

 harvesting by machinery, reproduces after cutting, and yields a paper- 

 pulp of better quality than that from other milkweeds. The per- 

 centage oi rubber present averages about as high as that of the others 

 and is sufficiently fluctuating to indicate that superior high-yielding 

 strains coiJd be produced through breeding and selection. This 

 building-up of the rubber-content will be an essential preliminary to 

 the utihzation of any of the plants here considered. It would be 

 futile to attempt the profitable production of rubber on the basis of 

 the percentage content thus far found in American species. 



