per annum) and a temperature of 70°-90° F. These con ditions are obtained over wide areas in the East. Eventually Sir Joseph Hooker, Director of the Royal Botanical Gardens, Kew, London, interested himself in the problem, and in 1873 2,000 Hevea seeds from the Amazon were delivered to Kew by a Mr. Farris. Only a dozen germinated, and six sent to the Royal Botan ical Gardens, Calcutta, did not thrive. Arrangements were then made for further supplies of seeds. The most successful col lector was H. A. Wickham (now Sir Henry Wickham) who dis played much enterprise and care in successfully bringing to Kew a consignment of 70.000 seeds of Hevea brasiliensis. Hot houses were summarily emptied, and within two weeks of the arrival of the seeds in England there were over 2,000 young plants, nearly all of which were despatched to Ceylon, where they proved very successful.
After the establishment of Hevea trees in Ceylon steps were taken to distribute plants and seeds to other countries. Diffi culties were experienced in exporting seeds in a sound condition, and the problem was studied by H. N. Ridley in the Botanical Gardens at Singapore. He found that seeds packed in moist, powdered charcoal retained their fertility for a long time, and when shortly after the beginning of the twentieth century plant ers began to take an increasing interest in rubber, large quanti ties of seeds were distributed by this means from Malaya.
The countries producing the largest quantities of plantation rubber are Malaya, the Dutch East Indies, and Ceylon. Smaller amounts are also obtained from India, Sarawak, Borneo, French Indo-China, Siam and various parts of Africa. Owing chiefly to the demands of the motor car industry the production of planta tion rubber has made phenomenal progress. The first occasion on which a considerable amount of plantation rubber was offered on the market was in 191o, when the output reached i i,000 tons.
By 192o it was nearly 317,000 tons and in 1927 it amounted to 567,000 tons. In this period there were wide fluctuations in price, ranging from 125. od. per lb. in 1910 to 71d. per lb. in 1921.
While the production of plantation rubber has continued to increase that of wild rubber has decreased until in 1927 the world's production of all grades of wild rubber was only 6% of that produced on plantations. The reason for this is that not only is plantation rubber of good quality, comparable with that from the Amazon, but it is put on the market in a clean, dry condition.
The structure of what is popularly known as the bark is of con siderable importance in Hevea brasiliensis, because, as already in dicated, the latex vessels in this part of the tree are the chief source of the world's rubber supply. The trunk of a tree may be divided roughly into an inner portion of wood and an outer por tion of bark. At the junction of the bark and the wood is a layer of cells about the thickness of a sheet of paper, known as the cambium, which appears as a slimy layer when the bark is torn away from the tree. This layer is the seat of growth, on the one hand adding new cells to the wood and on the other new cells to the bark. Next to the cambium and in the soft portion of the bark are found the latex tubes. Outside the soft bark is a hard portion where there are comparatively few latex tubes. The whole is protected by an external layer of cork. The diameter of the latex tubes is considered to be about 0.0015 inch.