230 



which do not coagulate, so that it is difficult to avoid the inference 

 that the percentage of albuminous matter is not constant or that 

 it has been incorrectly determined. 



At La Zacualpa was witnessed still another method of coagula- 

 tion by which all the non-volatile constituents of the latex are 

 retained. The latex is spread in a thin coating upon the large 

 banana-like leaves of a species of Calathasa, laid out on the hot 

 bare ground in the open sun. This exposure to heat, light, and 

 air turns the milk dark with great rapidity, and in a few minutes 

 it has become firm enough to permit a second layer to be spread 

 on. Subsequently two of the leaves have .their rubber-covered 

 faces pressed together by being trodden upon, and the rubber 

 adheres to form a single leaf-like sheet from which the leaves 

 themselves are easily stripped away. 



COAGULATION OF SCRAP RUBBER. 



Whether due to a varietal difference in the trees or to climatic 

 or other differences of the external conditions, it seems to be a 

 general fact that on the more continuously humid eastern slope of 

 Central America the milk of Castilloa does not run from the trees 

 in quantities which can be collected and treated by improved 

 methods of coagulation, but hardens in the cuts made by the 

 rubber gatherer, who does not carry home the milk but returns in 

 a day or two to pull out the dried " scraps," as rubber obtained in 

 this way is called in the trade. As both the quality and the price 

 of scrap rubber are satisfactory, the chief objection to this method 

 of harvesting is the greater number of cuts in the tree and the 

 greater amount of labour necessary to collect it, though the latter 

 objection is somewhat counterbalanced by avoiding the work of 

 coagulation. The principal point is the amount obtainable, and 

 this depends upon the question of climates and varieties rather 

 than upon that of coagulation. According to Professor H. Pittier, 

 6 pounds of scrap rubber are sometimes taken from a single wild 

 tree in Costa Rica ; but while this amount is considerable it is 

 much less than that claimed by Koschny for the same country. 



YIELD OF CULTIVATED TREES. 



It may be said that at the present stage of this inquiry 2 pounds 

 per tree is looked upon as the reasonable maximum yield to be 

 expected from adult trees of twelve years and upward, growing 

 under favourable natural conditions. This is the highest estimate 

 which is known to the writer as having been made by reliable 

 planters of intelligence and experience ; and some such hold that 

 the probabilities lie nearer to half a pound than to 2 pounds. It is 

 appreciated that this estimate is much smaller than many claims 

 based on wild trees and that it is much larger than the results 

 reached on some of the earlier plantations would seem to promise. 

 The estimate is not, however, made as an average of all published 

 figures, but is reached rather by the elimination of unwarraiited 

 expectations from one end of the series, and from the other of 

 disappointments due to adverse local conditions. 



