42 THE PRINCIPAL RUBBER- YIELDING PLANTS 



For furtlier pcarticulars regarding the above rubbers 

 reference should be made to Imperial Institute Selected 

 Reports on Ruhher and Gutta Percha, pp. 392-400. 



18. The American rubber vines belonging to the natural 

 order Apocynaceae. 



The Apocynaceous rubber vines are represented in 

 America by the genus Forsteronia, of which there are two 

 species, F. floribunda, G. Don, and F. gracilis, Miill. Ai-g. 



F. floribunda occurs freely in the limestone districts of 

 Jamaica, and, as will be seen from the followmg analysis 

 made at the Imperial Institute, it fm^nishes rubber of good 

 quality : 



Per cent. 

 Caoutchouc . . . . 888 



Resin 



Protein . . , , . 16 



71 

 Insoluble matter 

 Ash 



1-4 



The rubber is, however, difficult to obtain from the 

 vmes by tapping. 



/.u A,^^".^ber of rubber-yielding vines occur in some 

 of the Pacific islands. In Fiji rubber is obtained from 

 several species of Alstonia, the principal of which is stated 

 to be A. plumosa, Labill., and in British New Guinea 

 rubber vines also occur and are tapped by the natives 

 20. Dyera costuhta, Hook, f., the Jelutong tree 

 The mferior rubber-like material known as Jelutong 

 or Pontianac is derived from several species of Dyera the 

 prmcipa of which is Dyera costulata. The trees occur 

 in the ]\ralay Penmsula, Sumatra, and Borneo. 



Dtjera costulata is a very large tree, the trunk of which 

 may attain a diameter of 4 to 6 ft. It yields a large 

 quantity of latex which the natives coagulate by stirring 

 with a little kerosene, after addmg a small quantity of 

 powdered gypsum. The product is usually prepared in 

 the form of large balls or cheese-shaped masses. It is 

 white and granular, and when freshly prepared contains 

 as much as 60 per cent, of moisture. The dry material 



boi ;;'"' ^^ P"' ''''^- ^^ ^«o"tchouc, the remainder 



ocuig resin. 



