Central American, or Panama rubber is from a tree called Castilloa elastica, which grows ten degrees north of the equator. The rubber has not the strength of Para, and brings a lower price. It is the tree of Mexican and Honduras plantations.
A tree that reaches sixty feet in height, and yields rubber almost equal to Para, is Sapium Jeumani, that grows in Colombia and Guiana. In cultivation, it does surprisingly better than in the wild.
The "India rubber" plant of the northern greenhouses, Ficus elasticus, is the Assam rubber tree in its East Indian forest home. It may begin life as an air plant, fixing its roots in the crotch of another tree in which a seed has lodged. A shock of aerial roots strike downward, and reach the ground, after which the top depends upon food drawn from the earth, and the supporting host tree is no longer needed, for the rubber tree by this time has a stiff trunk, and is able to stand alone.
Assam rubber is not inferior to Para, except that it is not so carefully gathered, and comes dirty to market. The mountain trees are the only ones that produce first quality rubber.
The Silk rubber is a tree sixty or seventy feet in height, as it reaches maturity in the forests of Africa. It crosses the central part of the conti nent, from east to west, the seeds wafted away on the long, silky filaments that give the tree its name. "Funtum" the natives call it, and the scientific name is Funtumia elastica. The trees
are tapped by the herringbone method, the latex (milky juice), collected in hollowed-out logs, and covered with palm leaves. The water is absorbed by the porous wood, and the spongy rubber that remains is kneaded into balls and sent to market.
In the West African forests the natives are practically slaves to the agents of the company that holds the concession from the government that rules the district. King Leopold of Belgium has been held personally responsible for much of the abuse that has terrorized the blacks.
Several different species of woody climbers of the genus Landolphia, near relatives of the Funtum tree, yield rubber when tapped. The latex is spread out, coagulates, and layer on layer, is prepared for market. The old method was to cut down the vines to drain their juices. As they grow on forest trees, they form a jungle in which it is difficult to collect the latex.
The rootstocks of certain Landolphias and other plants, and the tuberous roots of the Guayule plant of Mexico and the Ecanda plant of West Africa yield "root rubber," which is ex tracted by breaking them up in hot water, and later separating the waxy rubber from the residue.
It is not likely that these plants will be used when the growing of plantations and the harvest ing of rubber from wild forests are put on a sound economic basis.