Funtumia elastica and its cultivation in Africa have been made the exclusive subjects of a recent book by C. Christy (The African Rubber Industry and Funtumia elastica). From this work the few remarks here given are partly summarised, and for fuller information reference may be made to the original source.
Some description of the species itself was given in Chapter II of the present work. The seeds retain their vitality well. They are very small, with a plume of long silky hairs, and one ounce of seed is sufficient for 20 square yards of seed bed. As germination at even distances cannot be guaranteed, the seedlings may with advantage be transplanted to a second seed bed prior to planting out in the field. The further operations of planting and cultivation are similar to those adopted in the case of Hevea.
Very close planting is recommended, to be followed by subsequent thinning. Close planting is said to be necessary in order to obtain straight clean stems, to obliterate lower branches which would interfere with tapping, and in order to minimise the cost of weeding. The thinning subsequently undertaken gradually leads to a distance of 12 by 12 or 15 by 15 feet at six or seven years of age. The trees are deep rooting; consequently manuring and cultivation have less effect upon growth and yields than in the case of Hevea. A fair yield is obtained from the sixth year onward. The average growth in plantations is said to be of the same order as that of Hevea, the increase in girth being from three to four inches per annum.
As in the case of Castilloa, the trees can only be tapped two or three times in a year, and great care has to be exercised in order to avoid damage to the bark. The method of tapping recommended by Christy is by cutting shallow conducting grooves on a half-spiral system. The slanting grooves are then to be pricked with a thin-bladed spur pricker. Eight inches is regarded as the best distance between the lateral channels.
The trees are first tapped during the sixth year. They are then tapped twice a year until they are eight years old, and afterwards three times a year. The later cuts are made about two inches above the old, and a fresh vertical channel is made at each tapping. On old trees the tapping may be carried to a height of 30 feet.
In a particular series of experiments, about five ounces of dry rubber per tree was obtained by tapping to a height of 30 feet on the double half-spiral system. The average girth of the trees concerned was 28 inches. Christy gives the following estimates of the average annual yield per tree under plantation conditions.
Age, years ......
Dry rubber, ounces ...
Coagulation is effected by simple dilution with water or by the use of various reagents, amongst which tannic acid, formalin and hydrofluoric acid are said to be specially effective. The fresh latex is neutral in reaction or very slightly acid, and acetic acid alone does not produce coagulation. Centrifugal machines are also useless, probably on account of the very small size of the latex globules. The physical properties of the rubber are found to vary considerably, according to the nature of the chemical reagent employed.
Christy regards Funtumia as better suited than Hevea for growth in African plantations. It is less liable to the attacks of insect pests, and is much cheaper to cultivate. It is also considerably cheaper to tap, owing to the relatively large yields obtained at a single tapping. Plantations have already been opened on an extensive scale in Kamarun, and the cultivation is under trial in Southern Nigeria and in other parts of British West Africa.
The introduction of Funtumia into countries outside Africa has not generally been attended with much success, for in other climates the plant appears to suffer widely from the attacks of insects. At Pera-deniya the growth of the trees was found to be very slow, largely owing to the depredations of a leaf-rolling caterpillar, which led annually to the complete defoliation of every branch.