EARLIER INVESTIGATIONS. 11 



covery of new rubber plants find their way into the literature. These 

 reports sometimes cause considerable trouble through the time con- 

 sumed in establishing their falsity, and in some instances they have 

 been used to lure investors into fraudulent commercial enterprises. 

 The more persistent of these reports refer to the following plants : 



Ocotillo (Fouquieria splendens), a tall shrub of the southwestern 

 deserts, has been reported a number of times as a rubber plant and 

 money invested in its utilization for this purpose. However, very 

 careful chemical examination shows beyond doubt that no rubber is 

 present. Analysis by the usual method as described later gives no 

 return in the benzene extract. Furthermore, when the pulverized 

 material is extracted with benzene, the residue after evaporation is 

 entirely soluble in acetone, thus indicating again that no rubber is 

 present. Ocotillo contains considerable amounts of waxes, resins, and 

 similar substances, some of which are now being manufactured on a 

 commercial scale, according to Pearson (1920). 



Various species of cactus are stated to contain rubber, but no 

 evidence of its presence has been found and the chemical nature of the 

 plants does not encourage its expectation. Opuntia vulgaris was one 

 of the species mentioned, with the statement that rubber was obtained 

 from it in Arizona. This plant grows nowhere in the Southwest. 



Claims also have been made for certain ocean kelps, especially 

 Macrocystis pyrifera, as rubber plants, and companies formed in 

 southern California to exploit them on this basis. A detailed chemical 

 study of the organic constituents of kelps has been made by Hoagland 

 (1915), who reports that carbohydrates or analogous bodies make up 

 the principal portion of the organic matter and that these carbo- 

 hydrates are complex colloidal substances which would ordinarily be 

 classed among the vegetable gums or pectins. Thus the rubber present, 

 even if it occurs at all, which seems extremely unlikely, would be so 

 small in amount as to be negligible. 



During the period of high rubber prices much effort was made to 

 find plants similar to guayule, and many species of the Southwest and 

 of Mexico were investigated in this connection. The one reported 

 most frequently, presumably because of its superficial resemblance to 

 guayule, together with its gummy and resinous nature, was the brittle- 

 brush or incienso (Encelia farinosa) . Repeated analyses of this plant 

 prove conclusively that rubber is not present. A closer relative of 

 guayule, namely, themariola (Partheniumincanum), of Mexico, carries 

 but a very meager amount of rubber, according to Lloyd (1911). 







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