PERHAPS no statement in regard to the source of our commercial rubbers is more surprising to one unacquainted with this particular field than that over 200 species of plants contribute to the sum total of the crude material which comes to the market. Indeed, that "rubber plant" which is frequently used as a household decoration is usually thought to be chiefly responsible, but this is far from the truth. This same rubber plant, however, furnishes us with a point of departure for the present account in the fact, well known to every one who has but slight acquaintance with it, that when injured, a milky fluid (latex) escapes, which, on drying, becomes translucent, and displays in some degree the familiar properties of india-rubber, or caoutchouc.
Diverse as are the plants which furnish caoutchouc, until a few years ago practically all of it was obtained by "tapping." This consists in cutting into the bark of the plant, and collecting either the milk (latex), to be coagulated immediately or later by various methods, or the strings and masses of coagulated latex adhering to the wound or elsewhere. Among the latex plants the only exception worthy of mention is the so-called grass or root rubber of the Congo. The rhizomes of the various species, which, because of their position, can not be tapped, are collected and dried, whereby the rubber is coagulated in the latex-tubes. It is subsequently extracted mechanically by heating, under such conditions as to separate the rubber from the fiber. It will appear evident that whenever the rubber exists as such within the plant, either as the result of coagulation or for any other reason, other methods than that of tapping must be resorted to for its extraction. The practise in the case of the root-rubbers suggest comminution of the
- For a full account see F. E. Lloyd, "Guayule, a Rubber Plant of the Chihuahuan Desert," Carnegie Institution of Washington, Publication 139.