The duration of the life of the tree is not known. The oldest trees in cultivation are about thirty-five years of age and show no signs of weakening ; and there are said to be some trees in the Amazon region which have been tapped for eighty years.
It was formerly thought that the Hevea requires swampy river-side lands, but the discovery of forests of it in high lands shows that a moist situ ation is not essential. That it thrives in gravelly soil and stands drought well has been amply proved. The better the land, however, the better the growth, and on well-drained river-side lands it certainly reaches a larger size than on dry ground. The tree thrives in the open, but grows faster when slightly shaded in its younger stages by trees of similar habit. (Hart.) The trees should fruit in their fifth year. The flowering seascn is preceded by the fall of the leaves, which in young trees takes place all at once. Older trees shed their leaves more irregularly.
Tapping. Many methods of tapping are now in use, and it is probable that as the industry pro gresses other methods may be found to which those in use will eventually give way. In the original forest the life of the tree is but little regarded, and generally the collector takes all he can, to get which the trees are badly mutilated and usually die. It is evident, therefore, that very careful measures are necessary on cultivated estates, not to injure the trees if continuous crops are to be secured. While the trees have large recuperative power, yet it is certain that excessive wounding for bleeding purposes must tell on them and event ually diminish the yield, if indeed the trees do not succumb altogether. (Hart.) Tapping may begin in the sixth year with Hevea, but much depends on the size of the stem at that age. The rubber from young trees is weaker and lighter than that from older trees, which is valued more highly. It is watery and contains a consider able proportion of resinous matter, a feature which disappears as age advances.
The most convenient and satisfactory method of tapping the Para rubber tree is the herring-bone system (Fig. 793). A vertical incision is made in the bark from as high as a man can conveniently reach to within a few inches of the ground, and as nar row as possible, as it is required only to con duct the milk to the cup inserted by its edge at the base of the cut. On
either side, sloping cuts are made alternately about six inches apart, connecting with the central cut. The milkruns from these side cuts to thecentral chan nel and so into the cup.
Each day a thin slice is taken off the lower side of each side cut till the milk ceases to flow or till the cut is about one and one-half inches wide, when tapping is stopped and the wound allowed to heal, which it does in about six months. Wounds may be dressed with coal-tar.
Tapping is done all the year round, and is best per formed in the early morning at daylight, or in the evening. The former gives the largest yield. Some growers prefer to tap during wet weather, on the theory that the sap flows faster then, and because the additional moisture delays coagulation and thus facilitates gathering. In dry weather the latex coagulates in the cuts and stops the flow.
The instruments used for cutting the bark are very varied, new ones constantly being invented. Especially in old trees, a mallet and a chisel are perhaps the best and most easily used. The cups for catching the milk are made of aluminum, with a rounded base, and contain four or eight ounces.
The milk runs for half an hour or so and then stops. The cups are collected and their contents poured into jugs or other large vessels to carry to the curing shed. It is advisable to put a little water with a drop of formalin into each cup before fixing it to the tree, to avoid coagulation in the cups, which sometimes occurs. The latices of all trees should be strained through a fine wire mesh to remove the impurities inseparable from the bleeding process.
Preparing.—Rubber may be made in various forms, the best of which are biscuit, crepe or sheet, and block. For biscuit, the latex, after being strained through muslin or wire gauze to remove any dirt, is poured into enameled iron plates. A few drops of acetic acid are put in each plate, and the milk stirred. The plates are covered and put aside for about twelve hours, when the latex is found to be set, and can be taken out in a cake. It is then put between rollers and rolled flat, and laid away on a rack to dry, in a cool, dry place. The drying usually takes some weeks. When quite dry the biscuits are packed in wooden boxes for shipment. If in drying mold appears, the biscuits are wiped with a rag moistened with formalin.