The rubber of both _Hevea_ and _Castilla_ is produced from the milky juice or sap of the trees and is actually a wound response. As the trees are tapped the _latex_, as the milky juice is called, runs out of the wound and upon reaching the air coagulates. This material is removed and a new wound made, a process which is repeated for several years. There is still work to be done upon the problem of how often plantation trees should be tapped to get the greatest flow of latex without injuring the tree, but in many plantations it is done every day or every other day in the season, some rubber planters allowing a resting period during leaf fall, others again tapping almost continually. The actual wound is made by removing just enough bark to induce a flow of latex, but not until the wound is completely healed, a process taking from four to six years, can that particular part of the bark be cut again. With almost daily tappings the problem of finding fresh pieces of bark into which the cut may safely be made has been developed into a fine science. In the wild trees of Brazil it is still done by natives, probably rather wastefully. Rubber plantations in the tropical regions of Asia now total over a million acres, as compared to only slightly over 200,000 acres in the American tropics and from all other non-Asiatic sources. Of this probably 100,000 acres are in Africa. At the present time nearly half the world’s supply of rubber comes from these plantations, the balance still coming from Brazil.