A/0> Hawaii Agricultural Experiment Station, HONOLULU ITH, Special Agex RESS BULLETIN No, OSTORY RUBBER IN HAWAII. > A comparatively new industry, the cultivation of rubber- producing plants, now engrosses the attention of planters in all tropical lands. There are probably more new areas being planted to rubber than to any other single crop, and much cap- ital formerly invested in coffee, cinchona, tea, cotton and sugar is being diverted to this new industry in the hope that the profits will be greater than are now derived from older estab- lished enterprises. For those interested in new rubber plantations in Hawaii the following notes in regard to the plants which are the chief sources of the world's rubber supply may be of value. x In 1900 Africa produced 16,000 tons of rubber, America 31,466 tons, and Asia and Oceanica 2.339 tons, a total of ap- proximately 50,000 tons. The world's production was esti- mated at 53,887 tons in 1902. 55,603 tons in 1903 and 61,759 tons in 1904. The average price for "Tine Para'' in Liverpool has risen from 75 cents per lb. in 1902 to $1.14 in 1904, and has not been less than $0.75 since 1895, and has not fallen below $0.60 since 1877. This rise in price has been due to the greatly increased demand for rubber in the arts and industries without any corresponding increase in the source of supply. The out- look is that the price of rubber will continue to rise until either the price becomes prohibitive thus curtailing demand ; or, an artificial substitute for this valuable product is produced syn- thetically in the chemical laboratorv; or, until the world's cul- 1 This is mainly a compilation from the extremely valuable monograph on the rubber plants of the world by Peter Reintgen : " Die Kautschuk- pflanzen. Eine Wirthschaftsgeographische Studie,'' Tropenpflanzer. Vol. VI. May, 1905. tivated rubber plantations begin to yield to the full extent of their capacity. Xo extensive new rubber forests are likely to be discovered, although investigators are almost daily adding names to the list of plants from which rubber may be secured. New rubbers require much experimentation before their relative commercial ? % value becomes established. Artificial rubbers may resemble the natural article in some «V. tT#? ne °^ ^ s characteristics but none have thus far been produced ' % \ which have the requisite elasticity. As to the third solution, while there can be no doubt that cultivated rubber plantations may ultimately supplant the prod- uct of the wild trees, it will undoubtedly be a matter of decades rather than years before even a parity between supply and de- mand is reached. In the meantime the question arises, if we are to plant rubber, to what particular variety shall we pin our faith. A consideration of the climatic conditions under which the various natural rubber producing plants thrive will therefore first be necessary. AMERICAN SPECIES OF RUBBER PLAXTS. Para Rubber. In 1904 nearly fifty per cent, of the world's supply of rubber came from the Amazon valley and the major share was classed as "Para." Para rubber is, has been and probably will contnue to be the standard of excellence with which all other rubbers are compared. It is in the main derived from a large tree, Hevea braziliensis, Muell. Arg., which grows wild in the trop- ical forest on the south bank of the Amazon and its tributaries, the Rio Purus, Rio Jurua, Rio Negro, Rio Madeira, and Rio Javary-Iquitos. So far as known, Hevea braziliensis only rare- ly occurs on the north side of the Amazon, but its place is there taken by other species of Heveas which yield rubber of inferior quality and secondary value. Hevea braziliensis is a stately tree often reaching the height of 130 feet with a trunk 3 to 1 feet in diameter, the crown not very large but somewhat dense. The leaf is compound with three oval, sharp-pointed leaflets, dark-green above, bright-green on the under surface and rather prominently nerved. The flowers are small, yellowish-green, and the fruit a 3-celled capsule with 3 seeds as large as hazel- nuts. The trees are sparsely scattered through the tropical jungle over a region as large as Europe, and it is said that the native rubber collectors consider that a remarkably rich rubber dis- trict where the rubber trees average one to the acre. The mean annual temperature of the regions is about 83° F., with an annual range between 73° and 95°. The rainy season begins in October. By January the whole region for 2,000 miles is more or less submerged and the floods do not begin to disappear until June. During the "dry" months, July, August and Sep- tember, there are frequent thunderstorms. The home of this tree is a hot, steamy, truly tropical, rich alluvial plain, almost under the equator and only slightly elevated above sea level. The tree seldom occurs at elevations greater than 600 feet. Its native habitat, so widely different from the climate of Hawaii, undoubtedly precludes the probability of its successful cultiva- tion in these islands. There are eight or ten other rubber-yield- ing species of Hevea, some of them undescribed by botanists, all native of the upper Amazon valley. vVhile some of these grow at higher elevations and in lands not periodically submerged their total yield is comparatively inconsiderable in quality and amount. White Rubber. This is produced by a number of species of trees of the genus Sapium, native in the north-western portion of the South American continent. Sapium, Tolirnense, Hort., is a native of the mountains in South Western Colombia, making its best growth at an altitude of 3700 to 6000 feet . The tree is said to grow with extraordi- nary rapidity, reaching a height of fifty feet with a trunk one foot in diameter in six years. It will grow at a higher elevation than coffee. The rubber is of very excellent quality. This is certainly a promising variety for introduction into Hawaii. Sapium verum Hemsl. A forest tree 60 to 75 feet high with a trunk 3 feet in diameter, native to Ecuador and southern Colombia. It reaches its best development at an elevation of 5,500 to 7,500 feet and grows up to 10,000 feet. This tree is the principal source of the "caucho bianco" of Ecuador. Sapium stylare AEuell. Arg. A large forest tree occurring at an elevation of from 3,000 to 6,000 feet on the wet mountain slopes from Venezuela to eastern Ecuador. The mean tem- perature of the region where it grows ranges from 56 = to 61° E. Other species of Sapium growing under truly tropical condi- tions at lower elevations are S. tapuri Ule.. S. eglandulosum Ule, S. utile Preuss, and S. Marmieri Huber. The milky sap of the latter is poisonous. These species all require higher temperatures and a greater degree of humidity than is found in Hawaii. Black Rubber, or Central American Rubber. The chief source of this rubber is Castilloa clastica Cerv. It is a native of the western slope of the Andes of Peru and Ecua- dor up through Central America to Mexico. The tree grows to the height of 40 to 60 feet in the open, but often reaches 120 to 150 feet in height and 6 feet in diameter in the dense and hot tropical forests. Unlike Hevea it will not stand wet feet but requires good drainage. It is never found in wet or swampy localities and grows best at the lower elevations in hot, sheltered inland valleys. In the equatorial belt Castilloa oc- curs up to 2,500 feet but at 15° either side of the equator does not grow well above 1,600 feet. It requires rich alluvial well- drained soils, high temperatures and shelter from winds. The optimum mean annual temperatures for the growth of this tree range from 77° to 82° F. It grows in Mexico where the mean yearly temperature is 72° F. and will stand a much lower one, but as the temperature and humidity decrease the growth of the tree is slower and the yield of rubber rapidly diminishes. The leaves of Castilloa elastica are heart-shaped at the base, entire, bright-green and shining, those of young trees 20 inches long by 7 inches wide, those of old trees 6 to 12 inches long by 2 1-2 to 5 inches wide. The trunk of the tree is wing but- tressed at the base. Rubber collectors distinguish 3 varieties depending on the color of the bark and twigs, but botanically all are considered one species. Castilloa elastica has been widely planted. Five hundred thousand trees of this variety have been planted in the vicinity of Bluefields, Nicaragua, during the last seven years. The first of the planted Castilloa forests in Nicaragua has been tapped this year. Six thousand seven-year-old trees yielded 534 pounds' of rubber, an average of 1 1-3 ounces per tree. A few of the largest were tapped repeatedly at 2-week intervals without in- jury and yielded an average equal to that secured at the first tapping. In the regions climatically suited to it Castilloa is considered one of the surest and most reliable species in the cultivation of which it is safe to invest the large capital re- quired to plant and care for an artificial forest up to the time when dividends may be expected. However, it is doubtful whether its cultivation should be attempted on more than an experimental scale in Hawaii. Our mean annual temperatures and mean humidity are too low, and also the islands lie within the zone of the trade-winds, and lack the tropical climate of other island groups in equal latitudes. Ceara Rubber is derived from a small tree usually (in Ha- waii) not exeeediug 25 to 30 feet in height. Manihot Glaziovni Muell. Arg. This tree is a native of southern Brazil. It grows on hot desert-like sandy plains and along the granitic ridges in a region devoid of running streams and with only a sparse cover of desert shrubs and low trees. The mean annual temper- ature of this region ranges from 82° to 90° F. The rainy sea- son resembles that of Hawaii in that there are only occasional rains during the wet months from Xovember to May, or June, but differs from Hawaii in that the rainy season comes in sum- mer. Although the tree is at its best in this hot desert country it extends inland to the foot-hills, where the rainfall averages about 100 inches and where the night temperatures often fall to 60 c F. or less. Like Castilloa elastica, the Ceara tree re- quires good drainage and never thrives in wet or swampy soils. Ceara rubber trees will grow in a very wide range of situa- tions. It makes an extremely rapid growth in Hawaii, thriv- ing from sea level up to 2,500 feet on both the dry and wet sides of all the islands. The tree is being largely planted in all tropical and sub- tropical countries. The seeds are about the size of small plum pits and mottled like castor bean seeds. When planted they take a long time to germinate, unless the hard, stony outer coating is filed or abraded. Plant the seed where the tree is to grow either at irregular intervals, if in gulches or along stony ridges or other waste land, or if tillable land is to be used plow and prepare the whole field, or plant in a hole, as is often prac- tised in the case of bananas. The distance apart should be from 6 x 10 to 12 x 15 feet, which would give from 240 to 726 trees per acre. If tillable land is used it will pay to culti- vate and fertilize. On gulch, mountainous and waste lands the weeds and grass must be cut out and a space hoed around the foot of each tree as often as necessary. A number of Ceara rubber trees were planted in 1893 on the land now occupied by this Station. A tree standing alone near the Tantalus road in the upper forest in the midst of a clear- ing, and which has been somewhat spasmodically cared for is about 40 feet high with a trunk 10 inches in diameter. Other trees planted along the trails and absolutely neglected for 12 years, overgrown by lantana and over-shadowed by Eucalyptus are now little more than 12 to 15 feet high with a trunk the size of a man's finger. So it pays to take care of trees even though common report has it that "no cultivation is required.' 7 Pernambuco Rubber. This formerly unimportant but of late years much-talked-of rubber is derived from Hancornia speciosa Muell. Arg. It is a medium-sized tree native to the dryer coastal plains and up- lands from Venezuela to southern Brazil and from the Atlantic to the eastern foothills of the Andes in Ecuador, Peru and Bolivia. Unlike the Ceara, this tree bears rubber in every part of the plant, in the bark, wood, leaves and green fruits. The milky sap which flows from wounds becomes rubber without other treatment than exposure to the air. The flow of milk sap is greatest during the summer months. Although Hancornia speciosa is of very slow growth it is being substituted for cof- fee by many planters in southern Brazil who see only small profits in that business for many years to come. The tree grows on a great variety of soils, and is easily propa- gated from cuttings. The leaves are about 2 inches long by 3-4 to 1 inch wide, acute at the base and blunt at the apex. The fragrant white flowers are about 1 inch across. The fruit is a greenish-yellow berry streaked with red, and is edible. The rubber is white and of very good quality. These species of rubber plants are the chief sources of the American rubber supply. The genera Hevea, Maniliot and Sa- pium belong to the Euphobiaceae or Spurge family, well known members of which are the Castor Bean, Tua-Tua and Cassava. The milky sap which yields the rubber is contained in milk tubes in the inner or growing portion of the bark. Hancornia belongs to the botanical family Apocynaceae, while Castilloa is one of the Moraceae, a family including the fig and bread-fruit. Of the 31,462 tons of rubber exported from South and Cen- tral American ports in 1900, 25,500 tons were derived from trees of the genus Hevea, 4,700 tons from Castilloa and Sa- ptum (40% Sapium and 60% Castilloa) and 1,250 tons Ceara and Pernambuco rubbers. AFRICAN RUBBER PLANTS. The African rubber supply is very largely derived from spe- cies of vines of several genera belonging to the botanical order Apocynaceae. L