156 



THE CULTURE OF THE CENTRAL AMERICAN 



RUBBER TREE, XL* 



{Continued from Bulletin for fune.) 



By O. F. Cook, Botanist in charge of Investigations in Tropical 



Agriculture, U. S. Department of Agriculture. 



DIRECTION AND SHAPE OF INCISIONS. 



The tubes which produce the milk of Castilloa and other rubber 

 trees are so slender and thread-like that the creamy liquid would 

 not flow from their cut ends if it were not forced out by pressure. 

 Some writers seem to have assumed that the liquid is actually com- 

 pressed inside the tubes, or that the walls of the tubes are stretched 

 by the liquid they take up. A more probable view is that recently 

 advocated by M. Lecomte, t that the pressure is due to the tension 

 of the bark, and that it is mostly exerted in a transverse direction. 

 If we add to this the fact that nearly all the tubes extend length- 

 wise, a transverse cut would reach the maximum number of these 

 and would thus for two important reasons secure more milk than 

 one of the same length in any other direction. A cut along the 

 trunk would be the worst, since it would reach the fewest tubes 

 and relieve the tension of the bark most. Oblique cuts are inter- 

 mediate, the more horizontal the better. M. Lecomte hesitates to 

 recommend transverse cuts lest they may prove injurious to the 

 tree ; but if a short transverse cut will bring as much milk as a 

 longer oblique gash there seems to be no real reason why it should 

 be more harmful, providing, of course, the tree be not girdled, or 

 too much bark be not cut away at one level. The practical diffi- 

 culty with transverse cuts lies in the fact that it would be much 

 more difficult to collect the milk, some of which will stay in the 

 cuts, while the surplus will run down the trunk of the tree in many 

 driblets instead of being brought together at the point of the V- 

 shaped incisions generally used. The desirability of making the 

 cuts as nearly transverse as possible should, however, be con- 

 sidered, and in districts where, as in eastern Guatemala, depen- 

 dence is placed entirely on the " scrap" rubber, most of which 

 coagulates in the cuts or on the surface of the trunk of the tree, it 

 may be feasible to make the cuts nearly or quite transverse. Indeed, 

 this is what Dr. Preuss describes as customary on the El Baul plan- 

 tation in Guatemala. 



For tapping they use an instrument made out of a bush knife (machete). The end 

 of the blade is for this purpose bent back until a groove is f^jrmed about broad 

 enough to lay a finger in. The cutting edge of this groove is well sharpened. 

 With this instrument the workmen tear horizontal gashes in the bark of the trees, 

 and indeed over a half or three-quarters of the circumference of the trunk. The 

 grooves are cut at distances of 1^ feet, one above another, up to the principal 

 branches. The milk at first flows out in drops, which fall to the ground. They 

 let these go to waste because the quantity is only small and this milk is very 

 watery. But in a minute or two the dropping ceases and the milk which then 

 oozes out is pulpy and remains in the turrows, where it hardens into strips 

 of rubber. In two days these strips are pulled out, washed, and dried in the shade, 



* Extract from thf U. S. Dept, of Agriculture, Bui. No. 49. Bureau of Plant Industry. 

 tJourn. d'Agri. Tropicale 10: 100. Translated in Agriculture Bui. Straits and 

 Federated Malay States, 1: 382. 



