RUBBERS AND GUMS 201 



as lo pounds of dry rubber in one year. The composition of 

 Castilloa rubber varies enormously, the resin varying from 6 

 to 50 per cent., as prepared by different methods. The usual 

 composition of Castilloa sheets obtained by the centrifugal 

 method is caoutchouc 91.5 per cent., resin 7.2 per cent., protein 

 0.5 per cent., ash 0.3 per cent., and moisture 0.5 per cent. 



The Assam rubber tree (Ficus elastica) is an evergreen 

 tree with smooth elliptical leaves, attaining a height of 12a 

 feet or more at maturity This tree is not much cultivated and 

 tapping is done, for the most part, in vertical rows of wedge 

 excisions made with a chisel or by means of deep V-shaped 

 cuts. The tree is tappable at 6 years of age. The latex is 

 coagulated by allowing it to stand for a long time or by the 

 addition of formalin. The yield from wild trees is about 

 50 pounds per acre and the composition of the rubber is caout- 

 chouc 77 per cent., resin 19.3 per cent., ash 0.5 per cent., pro- 

 tein 3.2 per cent., and moisture 0.5 per cent. Various other 

 species of Ficus have been exploited to some extent as sources 

 of rubber. 



Rubber vines include species of Landolphia, Clitandra, and 

 Cryptostegia. The species of Landolphia are woody climbers, 

 native of Africa with simple opposite leaves, sweet-scented 

 flowers, and large, often highly-colored edible fruit. These 

 climbers are of very slow growth and are not tappable until 

 they reach the age of 8 or 10 years. Some of them attain 

 a diameter of 12 inches and a length of 300 feet or more. The 

 rubber is collected by incising the bark and allowing the latex 

 to coagulate in the cuts or by collecting the latex in the bark 

 and coagulating it by heat, chemical reagents, or plant juices. 

 Sometimes trunks of Landolphia are pulled down from the 

 trees upon which they have been climbing, cut into short 

 lengths, and the latex allowed to run out. 



The most promising root rubbers are Landolphia tholloni, 

 Clitandra arnoldiana, and Raphionacme utilis. Rubber is ob- 

 tained from these plants by beating the separated bark or by 



