[Kew Bulletin, June and July, 1895.] The tree yielding Siam gamboge (Garcinia Hanburii, Hook. f.) is closely related to G. Morella, Desrouss., of Ceylon and Southern India. The former is a moderately large tree. The flowers are dioecious, the petals in both male and female flowers are fleshy and yellow. The fruit is the size of a crab-apple, yellowish green when ripe. The tree is found on islands on the east coast of the Gulf of Siam, as well as on the mainland of Cambodia and Cochin China. It is from these localities that practically the whole of the gamboge of commerce is obtained.
Gamboge is a gum resin yielded by the bark of the two species above mentioned. It is a powerful cathartic medicine, but its principal use is as a pigment in water-color painting. It is also used to give color to lacquer varnish for brasswork, etc. The most recent account of Siam gamboge is contained in a report on the trade of Siam for the year 1893, published by the Foreign Office (Annual Reports, 1895, No. 1,520). Mr. de Bunsen, Her Majesty's Charge-d'Affaires at Bangkok, was good enough to communicate to Kew specimens of the leaves of the gamboge trees, collected on the spot by Mr. Beckett, and, although the material is not quite complete, there is little doubt they belong to Garcinia Hanburii, Hook. f. The extract from the report is as follows:
"Gamboge is, next to gum benjamin, perhaps, the most interesting of Siamese products. Whilst gum benjamin is peculiar to a small belt of land in the north, gamboge is a resinous product, indigenous only in the islands and the seacoast of the Gulf of Siam lying between the tenth and twelfth degrees of north latitude. [The heavy rainfall of this coast seems necessary to the existence of the tree.]
"I recently had the opportunity of paying a visit to this part of Siam, and it may be of interest to describe the character of the tree and the mode of extracting the resin. The tree is known locally as 'Ton Rong.' It is found only in the islands of Koh Chang, Koh Kong and Koh Rong, and the mainland of the Indo-Chinese peninsula opposite these islands. The trees grow to the height of some fifty feet, and are straight stemmed with no lower branches, owing probably to the dense shade of the forests in which they grow. None of those I saw had a diameter of more than 12 inches. Ten years' growth is said to be required before the tree is ready for tapping. This is carried on by the Cambodian and Siamese islanders in the rainy months, from June to October, when the sap is vigorous, by cutting a spiral line round the trunk from a height of some 10 feet downwards to the ground. Down these grooves the resin wells out of the bark and trickles in a viscous stream into hollow bamboos placed at the base of the tree, and from these it is decanted into smaller bamboos, where it is left for about one month to solidify. To remove the gamboge, the bamboo is placed over a red-hot fire, and the bamboo husk cracking off, there is left an article known as 'pipe' gamboge. The trees can be tapped two or three times during one season, and at the end of the season their trunks present a curious network of intercepting spirals.
Care must be taken to prevent the rain-water mixing with the resin in the grooves, as any mixture of water causes honey-combing and black discoloration, and a consequent depreciation of from 20 to 30 ticals (2 l.) per picul in value.
The most valuable gamboge is that which is the least honeycombed or discolored, and is all the more difficult to obtain, considering the period of heavy rains during which the resin is extracted.
The bamboos contain on an average rather less than 1 lb. of gamboge, or about 170 bamboos to the picul. The price asked by the pickers themselves is at the rate of 2 ticals (3s.) for five bamboos full, and the local price is at the rate of 2 ticals (3s.) for three, or 65 ticals (4l. 18s.) per hundred, or about 8l 7s. per picul.
The whole output is sold to local Chinese traders and taken by sailing boat to Bangkok.