Before proceeding to describe the wild rubbers of Africa and Asia, mention must be made of one other American species of strikingly different habit from those so far enumerated. This is Parthcnium argentatum, the Guayule rubber plant of the deserts of Northern Mexico. The Guayule is a small shrub, rarely attaining a height of four feet or a diameter of more than three inches. The plant contains no latex, but granules of true rubber occur scattered through the tissues, especially those of the bark. The plants are gathered as a whole, and the rubber is obtained partly by a mechanical process of grinding and partly by chemical extraction. The exact processes employed are kept secret Guayule rubber was only first placed upon the market about 1903, when the demand for rubber was beginning to outrun the supply. By the end of 1909 the extraction of the rubber was said to be one of the most important industries of Mexico. The supply is however already diminishing, and this source of rubber can scarcely be regarded as a permanent one.