To obtain the latex, deep incisions are made near the base of the tree extending up the trunk. Small shallow cups are placed below the
Fig. 1.—Hevea brasiliensis.
incisions to receive the milk, each cup being attached by sticking a piece of soft clay to the tree and pressing the cup against it. The latex, of which each tree yields only about 6 oz. in three days, has a strong ammoniacal odour, which rapidly disappears, and in consequence of the loss of ammonia the latex will not keep for longer than a day unchanged; hence when it has to be carried to a distance from the place of collection, 3% of ammonia solution is added. The latex usually furnished about 30% of rubber.
To obtain the rubber, the latex is usually treated in the following manner. A piece of wood about 3 ft. long, with a flattened end forming a kind of paddle, is dipped in the milk, or this is poured over it as evenly as possible. The milk is then carefully dried by turning the mould round and round in the smoke produced by burning wood mixed with certain oily palm nuts; those of Attalea excelsa are considered best, the smoke being confined within certain limits by the narrowness of the neck of the pot in which the nuts are heated. The creosote and other products from the smoke no doubt act antiseptically and prevent to a large extent the subsequent putrefaction of the proteids retained by the coagulated rubber. Each layer of rubber is allowed to become firm before forming another; a practised hand can make 5 or 6 ℔ in an hour. In some districts a stout stick is substituted for the paddle, on which the rubber as it coagulates is wound cylindrically. The rubber thus prepared is the finest that can be obtained. The cakes when completed are, in order to remove them from the mould, slit open with a sharp knife, which is kept wet, and are hung up to dry. The Hat rounded cakes of rubber made in this manner are known in the London market as “biscuits.” They retain about 15% of moisture. The scrapings from the tree, which contain fragments of wood, are mixed with the residues of the collecting pots and the refuse of the vessels employed, and are made up into large rounded balls, which form the inferior commercial quality called “negro head,” and often contain 25 or 35% of impurity. The yield of rubber varies, but it is stated on an average to be 10 ℔ of rubber per tree, and if carefully tapped one tree will yield this amount for many years in succession.
Plantations of Hevea brasiliensis.—Hevea brasiliensis was introduced to Ceylon and Singapore from seedlings raised at Kew from Brazilian seed, specially collected by Mr H. A. Wickham in S. America. The seedlings rapidly developed and in most places in which they were planted grew into large trees which furnished satisfactory latex when tapped in their sixth or seventh year. Ever since plantations of Hevea have been made on an increasing scale in the Straits Settlements, the Federated Malay States and in Ceylon, and at the present time rubber plantations form the principal industry in these colonies. Successful plantations of Hevea have also been established in ]ava, Sumatra and Borneo. Many of these plantations have not yet reached the productive stager-that is, the sixth or seventh year. A large number of plantations in British Malaya and Ceylon are now actively exporting increasing quantities of rubber. Hevea seedlings were also introduced into India, but did not apparently succeed except in Burma and S. India. It may be estimated that between one and two million acres of land in the different countries referred to have been already appropriated for rubber plantations. Plantations are also being formed in British, French and German possessions in W. Africa and in the Congo, also in the tropical ortions of Australia. In certain districts of British W. Africa the Hevea which has been planted promises well, especially in the Gold Coast, where good yields of latex are stated to have been obtained.
It may be useful to summarize here the experience which has been gained in the formation of plantations of Hevea and in the production of rubber.
Hevea brasiliensis as a rule flourishes to the greatest extent at low altitudes on rich soil capable of retaining moisture. The nature of the soil appears, however, to be of secondary importance, provided that it is able to hold moisture and that climatic conditions of high and even temperature with considerable rainfall and absence of wind are satisfied. Although the tree is sensitive to such conditions it appears to possess a certain capacity of adaptation which should be borne in mind. Generally a low altitude is desirable, but good results have been obtained in Ceylon in sheltered positions at elevations of 3000 ft. and over, although at higher altitudes the growth of these trees appears to be slower. In many plantations besides catch crops (cassava, sesame, ground-nuts, &c.) other crops, such as tea, coffee, cocoa and tobacco, are grown with rubber. It is improbable, except in the early stages of the rubber tree, that this procedure will succeed; the rubber will ultimately dominate the position to the detriment and ultimate extinction of the other crop, whilst the growth of the rubber tree will be retarded. A partial exception may perhaps be made in the case of cocoa, when the two plants are placed not too closely in about equal numbers. In these circumstances it appears that satisfactory results may be obtained from both crops, at any rate fora certain number of years.
The experience of planters. in general is in favour of the complete removal of weeds from a rubber plantation. This practice, which involves periodical weeding, adds considerably to the cost of maintaining plantations, and, although justified so far by results, possesses several other disadvantages. During the tropical rain; the soil is liable, to a greater or less extent, to denudation, which becomes very serious when the land slopes; and in any case, the soil is apt to become impoverished by the loss of its soluble constituents. These disadvantages are at their maximum when the rubber trees are quite young. At a later stage the shade of the large trees compensates to a considerable extent for the absence of cover on the ground. Another disadvantage of uncovered soil in a plantation of young rubber trees is that the ground under the heat of a tropical sun rapidly loses its moisture. For this reason proposals have been made to plant in the place of weeds low-growing leguminous plants, the growth of which will not only prevent impoverishment and loss of soil during the rains and conserve moisture in the heat, but will also have the effect of enriching the soil in nitrogenous constituents through the power leguminous plants possess of absorbing nitrogen from the air through nodules on their roots. Among the plants which are being tried for this purpose are various species of Crotolaria, passion-flower, and the well-known sensitive plant of the East. The success of the method cannot yet be judged, but the experiment is one which deserves very full trial.
Fig. 2.—Tapping, herring-bone system.
One of the most important subjects in connexion with rubber plantations is the method to be adopted in tapping the trees for latex. The native methods in vogue in Brazil and Mexico are primitive and often injurious to the tree. At present it cannot be said that finality has been reached on the subject of the best method, giving a good return of latex with a minimum of damage to the tree. A method at one time largely adopted was to make a series of V-shaped incisions on four sides of the tree to a height of 6 ft. from the base—that is, within the reach of an ordinary man without the need for ladder or scaffolding; the latex obtained from the upper part of the tree is said to furnish less rubber and of poor quality. The latex is collected in cups placed at the apex of each V. Other systems are the herring-bone plan of a vertical channel
