Ceara rubber, Manihot Glaziovii, was the third species to be widely distributed to British possessions in the Tropics during the seventies. Introduced to Kew from North East Brazil by Cross in 1876, seeds or plants were sent out to most of the tropical colonies during the following year. In Ceylon this species attained a certain amount of popularity some years before Hevea came to be at all widely planted. Manihot was planted in the Trincomalee district in 1880, where, however, in spite of the richness of the soil, planting has made but little headway. Nevertheless, in 1883, no less than 977 acres were under cultivation with this product in Ceylon.
Difficulties of tapping, which have not even now been entirely overcome, soon led to a temporary cessation of planting, and after 1884 the interest in Manihot died away, owing to the small yields of rubber obtained. Samples of rubber from Zanzibar were unfavourably reported on in 1884, and further extension of the cultivation of Manihot in Africa was thus delayed. Recently, however, the species has been widely planted in East and Central Africa and in Angola, and good results are anticipated, owing to the fact that Ceara rubber grows well in a drier climate and at a higher elevation than Hevea.
Biffen, who visited the North East coast of Brazil in 1897, found large plantations already being opened in the Ceara district, at elevations up to 3500 feet. No recent reports regarding the development of these plantations are available. The methods of collecting the latex and preparing the rubber on plantations in Brazil appear to be similar to those applied to the wild trees. Tapping is generally carried out during the dry season by slicing the bark with a knife.
The Ceara rubber plant grows readily from either seeds or cuttings, but in order to ensure immediate germination of the seeds it is necessary either to file through the tip of the hard shell or to steep the seeds for some time in warm water. The early growth of the trees is very rapid, and it is often possible to begin tapping earlier than in the case of Hevea. Close planting is generally recommended, but this seems to be a mistake. Trees have been planted at distances of
15 by 15 feet in more than one district in Ceylon, and growth has been very rapid for the first two years. At the end of this time the branches met and formed a close cover, with the result that subsequent growth was very slow.
The structure of the laticiferous system of Manihot is closely similar to that of Hevea. The Manihots are the only other rubber-producing plants upon which tapping can be carried out at an equally short interval, and although the study of the subject has not been carried so far as in the case of Hevea, the phenomenon of wound-response seems to be closely similar in both.
Another advantage of Ceara rubber is that the plant grows like a weed, so that trees which have been injured in the course of tapping can be replaced with very little trouble.
On plantations, the hard outer bark is generally removed before tapping. Opinions differ as to whether tapping should take place immediately after the outer bark is removed or whether it should be delayed for a longer or shorter period. In Africa the method of tapping usually adopted is the primitive one of pricking or stabbing with a blunt thin-bladed knife The pricks are made about an inch apart in a vertical series. Sometimes die bark is first rubbed over with a freshly cut lime or lemon, in order that the latex may be coagulated on the bark by the citric acid thus applied. The strips of wet rubber formed upon the bark are collected by rolling them up on sticks or small wooden rollers.
When a thickness of about a quarter of an inch of rubber has been obtained, the rolls are slit up so as to form small sheets, which are subsequently washed and dried.
The method of alternate paring and pricking recommended in Hawaii has been found to cause considerable damage to the trees in Ceylon. Paring on the herringbone system has sometimes been found to give good results if not carried too far. If the paring extends over only an inch of bark, and a space of an inch is then left untapped before the next cut is made, the bark is generally found to heal satisfactorily. Rather wide shallow paring with a small gouge has given good results on Ceylon estates, and has been followed by perfect renewal. In many climates tapping can only take place during dry intervals in the wet season, since the trees drop their leaves during the dry season of the year, and then yield little or no latex.
Coagulation takes place on the simple addition of water. Very good samples of rubber, closely comparable with the best Hevea sheet in appearance, have been prepared by diluting the latex with an equal bulk of water and allowing it to stand until coagulation is complete. The further processes involved are precisely similar to those adopted in the preparation of Hevea sheets or biscuits.
A process which should be rigidly avoided is the mixing of the latices of Manihot and Hevea on estates where both products are cultivated. Such mixture leads to rapid coagulation without reagents, and to the production of a rubber which is excellent in appearance. Rubber of this kind is not, however, desired by manufacturers, and the mixed character of the sample is easily detected by experts. Manihot rubber requires slightly different treatment in manufacture from the produce of Hevea, and the mixed product is therefore unsatisfactory.
The yields from young trees appear to be similar to those from Hevea; in subsequent years, however, the increase in yield is not so great In Nyassaland in 1910 four hundred four-year-old trees are said to have yielded an ounce of dry rubber apiece from only two tappings, and the cost of collection was only 4d. per lb. In this case the tapping consisted of making vertical rows of pricks. At Peradeniya, Ceylon, experiments in paring were carried out on trees only three and a half years old at the beginning of the experiment, planted at the rate of 200 to the acre. About four ounces of rubber per tree were obtained in a year by 70 tappings. A yield of nearly 50 lbs. per acre was thus obtained at an earlier age than that at which a similar amount of rubber could safely be extracted from Hevea trees. The cost of production, however, was higli.
Among other species of Manihot, M. dichototna was introduced into Ceylon in 1908. So far, none of the new species have succeeded so well as Manihot Glazioviu The growth of the trees and the thickness of bark were poorer at equal ages, and in the few experiments made the yield of latex was less. Manihot dichotoma also suffered severely from the effects of wind of no great force; the trees were uprooted and branches were split off in every direction.