352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 5 



EXPERIMENTS IN EXTRACTION 



As a matter of fact, it was the extraction difficulty that was holding 

 back development of a guayule rubber industry. Unlike the hevea 

 tree, where the rubber-bearing latex is contained in perpendicular 

 tubes which flow when severed, guayule latex is stored in unconnected 

 small cells so that tapping the plant releases an inconsequential amount 

 of the fluid. 



The Indians chewed the bark, thus freeing the rubber and ag- 

 glomerating it in the mouth, but it was only after years of experi- 

 mentation with chemical extraction processes that anyone thought of 

 duplicating the chewing process on a large scale. Wm. A. Lawrence, 

 a chemist who had been employed by some American capitalists to 

 study the problem, and who also spent a couple of years searching 

 for a chemical solution, finally hit upon the mastication process. The 

 common "pebble" or "ball" mill of the mining industry was found 

 to be virtually made to order for guayule milling, and by 1904 the 

 guayule rubber business was firmly established in Mexico. 



A mill was also built at Marathon, Tex., about 1900, and operated 

 sporadically over a period of several years. It was dismantled in 

 the twenties because the accessible shrub supply had run out, but it 

 is interesting to note the truth of the old copybook maxim, "circum- 

 stances alter cases" — the Emergency Rubber Project has just com- 

 pleted harvesting some 2,400 tons of shrub there, regardless of in- 

 accessibility. Since the quantitj' did not justify building a mill there, 

 the shrub was shipped to Salinas, Calif., and processed in the project's 

 plant. It added about one-half million pounds of badly needed natural 

 rubber to the nation's dwindling stock pile. 



EXPERIMENTS IN CULTIVATION 



The principal guayule operator in Mexico early began to wonder 

 about the fate of the industry once the wild-shrub supply should 

 become exhausted. The plant is native only to the high, arid plateau 

 country from the Pecos River down through north-central Mexico, 

 where the average annual rainfall varies from perhaps 8 or 9 to 12 

 or 15 inches, and where plant growth is slow and reproduction scant 

 and uncertain. Guayule may live for 40 or 50 years, and it is said 

 that the average age of shrub harvested is about 15 years. It is a 

 poor competitor, hence grows only on sites not pre-empted by other 

 plants, such as eroded hillsides and ridges. Thus the plant occurs 

 in rather sparse stands in scattered patches, and on the open range 

 is not potentially a crop such as to intrigue a prudent husbandman. 

 Various attempts to improve reproduction by seeding, and even 

 by rough tillage of the soil, proved fruitless. 



