56 RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



XI. BY-PRODUCTS FROM ASCLEPIAS AND APOCYNUM. 



If financial success ever attends the growing of any native extra- 

 tropical North American plant on a commercial scale for its rubber, 

 this will doubtless be due in part to other products derived from the 

 same crop. The most promising of these by-products, as far as the 

 plants especially treated in this report are concerned, is fiber. It is a 

 fortunate circumstance that the botanical groups which include the 

 most important species from the point of view of rubber-content are 

 also characterized by the presence of bast fibers suitable to the manu- 

 facture of at least the cheaper grades of cloth and cordage. If not so 

 used, this fiber, which would be left after the extraction of the rubber, 

 could be utilized as pulp for the manufacture of paper. 



Fiber The cultivation of milkweeds, especially Asclepias syriaca 

 and A. incarnata, for their fiber has been advocated from time to 

 tune by enthusiasts, some of whom have claimed that commercial 

 success was assured. But the actual demonstration has never been 

 carried through in this country, although the former species is reported 

 as having been grown for its fiber in Syria and as far north as Upper 

 Silesia (Dodge, 1897), it having been introduced from America. It 

 is not impossible that, although the cultivation of th plants for their 

 fiber alone might be unprofitable, the utilization of the fiber after these 

 plants had been grown and extracted for their rubber might add very 

 largely to the net income and thus would be established an industry 

 based upon two important products. In this case two prime assump- 

 tions will be necessary, namely, that the proper time of harvesting 

 for the two products will coincide, and that one of these can be ex- 

 tracted without so treating the material as to make the recovery of 

 the other impossible. 



Certain considerations seem to render these assumptions reasonably 

 safe. For example, it is generally true of plants yielding bast fibers, 

 such as hemp and flax, that the best quality and yield are obtained if 

 they are harvested at about the time of maturity. Such plants are 

 often gathered when the leaves begin to turn yellow or when the seeds 

 begin to ripen. If this holds also for milkweeds and Indian hemp it is 

 a fortunate circumstance, for while there is not a universal concordance 

 in results, an examination of the tables of analyses presented in this 

 paper will show that milkweeds gathered when fully mature usually 

 carry more rubber than those of the same locality gathered earlier. 

 Regarding the extraction of both fiber and rubber from the same plant, 

 all that can be said is that experienced rubber manufacturers who have 

 been consulted state that they see no insuperable difficulty in the pro- 

 posal. In order to accomplish this, the mill should be so constructed 

 that the wet plants could be passed between rollers that would crush the 

 stems and separate the fibers without breaking them. If a chemical 



