LATEX-PRODUCING PLANTS 2>61 



the Soapberry Family and contain latex in both stems and leaves. 

 From the stem it is secured either by making gashes from which 

 the latex exudes very slowly or by the more usual method of 

 felling the tree and removing inch-wide strips of bark, about a 

 foot apart, from which the latex is caught in shells or large leaves. 

 This product is purified by boiling and washing to give the com- 

 mercial gutta-percha which is hard at ordinary temperatures, 

 softening at 77 degrees Fahrenheit and melting at a temperature 

 slightly above the boiling point of water. This type of gutta- 

 percha exploitation is very destructive to the trees, and is being 

 replaced by a plantation system which utilizes the leaves of a 

 shrubby variety of the gutta-percha plant. Leaves are harvested 

 and converted into a pulp while they are still fresh, after which a 

 treatment with boiling water washes out dirt and debris, leaving 

 the gum which is pressed into blocks. Gutta-percha is extremely 

 resistant to salt water and for this reason is, with its substitute 

 balata, irreplaceable as an insulator in the manufacture of sub- 

 marine cables. It is widely used in surgery and dentistry, and 

 in the manufacture of telephone receivers, pipes, golf balls, 

 electrical connections, and adhesives. 



Jelutong comes from the coagulated latex of several large 

 tree species belonging to the Dogbane Family and has been used 

 as an inferior substitute for rubber, gutta-percha, and chicle. It 

 is found growing in the swampy jungles of Malaya and Borneo, 

 and is utilized mainly in these regions. The trees are tapped in 

 much the same manner as those of the Para rubber tree, and 

 yield an amazingly large amount of latex. Unfortunately, the 

 latex consists of 70—80% resinous material and only 20-25% of 

 rubber. Jelutong was exploited as a source of rubber from 1910 

 to 1915, but with the rapid growth of rubber plantations it has 

 been practically neglected. More recentiy, development of re- 

 fining processes have led to its limited use as a substitute for 

 chicle in chewing gum manufacture. 



North American Rubber-producing Plants 



Commercial rubber, as may be seen from the foregoing 

 discussion, is practically all produced by large tropical trees and 

 woody vines. Several rubber containing species exist in the flora 



