19(5 



[April 1907. 



GUMS, RESINS, SAPS AND EXUDATIONS. 



THE GUAYULE RUBBER OP MEXICO. 



The form of Mexican rubber known as " Guay tile" has been known for a con- 

 siderable time, but it is only recently that full particulars regarding the plant from 

 which it is derived have been available, and that attempts have been made to 

 exploit the material on a commercial scale. The plant appears unlikely to be of 

 much importance a.' 3 a source ol rubber outside of Mexico, but as it possesses several 

 features of interest, a short account may be given of its characters and of the 

 methods employed for obtaining the rubber. The subject has been attracting con- 

 siderable attention both in America and Europe, and several notices of the plant and 

 of the projects put forward for its exploitation have been published recently in the 

 technical papers, the most important of these being an article by Dr. R. Endlich of 

 Mexico which appeared in Der Tropenpflanzer, vol. IX., 1905, p. 233. 



The Guayule plant is Parthenium argentatum, A. Gray, belonging to the 

 natural order Compositae. It is a small plant, varying from 8 to 40 inches in height, 

 with an average of about 21 inches, and has a much branched stem which bears small 

 silver-gray leaves and yellow flowerheads. In Mexico it flowers during September 

 and October. 



The plant occurs over a large portion of the " bush prairies" in Northern 

 Mexico, the most important districts being Chihuahua, the northern parts of the 

 states of Zacatecas and San Luis Potosi, the eastern part of Durango, and especially 

 the southern districts of Coahuila. It also extends northward into the United 

 States and is met with in Texas, New Mexico and Arizona. Its occurrence has been 

 reported from Southern Mexico, and also from Central America and Venezuela, but 

 these statements have not been confirmed and appear to be devoid of foundation. 

 The area in Northern Mexico, which includes the chief sources of supply, is stated to 

 be about 29,000 square miles. 



The Guayule plant is not so abundant or so widely distributed as was at first 

 supposed, owing to the fact that it was confused with another composite of the same 

 genus, Parthenium incanum, which occurs freely in the same regions. The Guayule 

 is found at altitudes ranging from 3,000 to 5,600 feet, and grows equally well upon 

 the plateaux or upon the hill-sides, being specially abundant on the lower slopes of 

 the larger mountains. The soil in these regions is usually very dry, often rocky and 

 contains a large percentage of lime. In most cases the plants occur scattered 

 amongst the other vegetation, but small areas are occasionally found where the 

 Guayule grows almost exclusively. It is thought from observations upon the wild 

 plants that under favourable conditions it will be possible to reproduce them freely 

 from seed, but experiments will be necessary before this point can be decided. 

 Some authorities believe that plants raised from seed attain the average size of the 

 wild plants in from 8 to 10 years, whereas others fix the time at from 12 to 15 

 years. Younger plants will furnish rubber, however, in proportion to their bulk. 

 The general opinion in Mexico is that Guayule plants gradually die off after reaching 

 the age of 15 years, but when the stems are cut down it is stated that new shoots 

 soon appear and furnish a new plant in due course. The average weight of the 

 plants as collected for the extraction of the rubber is not more than about 1 lb., the 

 minimum a bout 1 1 b. and the maximum about 6A lb. 



Parthenium argentatum is the only plant belonging to the natural order Com- 

 positae which is at present known to furnish rubber, and it is said to differ from 

 most rubber-yielding plants in the fact that it does not contain a well-developed 



