5 o RUBBER AND 



presumably serve a protective function. Active latex 

 vessels are distributed through a large part of the area 

 occupied by stone cells. Ultimately these also lose their 

 functions and dry up. Finally their remains are cut off 

 by layers of cork, and the rubber which they contain 

 is probably lost with the dry bark which rubs off from 

 the surface of the tree. 



When the outer part of the living bark is removed in 

 the process of paring, the cambium and young bark 

 remaining are stimulated in a healthy tree to still 

 more active growth, and the tapped area is said to 

 undergo renewal. There is evidence to show that the 

 effect of this stimulus is not confined to the area actually 

 tapped, but that the bark of neighbouring untapped 

 areas is also stimulated to more rapid growth, provided 

 the rate of tapping is not excessive. The time required 

 by the bark for renewing such a thickness as will permit 

 of a repetition of the paring process, varies according to 

 circumstances. Factors which affect the rate of renewal 

 are the age of the tree, its relative size, strength and 

 state of nutrition, and any external circumstances which 

 modify the nutritive processes, such as climate, soil, 

 elevation and rainfall. Renewal is also affected by the 

 method of tapping adopted, and by the extent to which 

 the tree has been tapped. For although moderate tap- 

 ping stimulates renewal, excessive tapping hinders this 

 process, and the more heavily a tree is tapped after 

 a certain rate has been reached the longer will be 

 the period which must elapse before tapping can be 



