102 PARA RUBBER. 



to six years onwards, having a minimum circumference of 20 inches, 

 may be expected to yield an average of one to three lb. of dry 

 rubber per tree each year up to their 10th year, and a higher yield 

 in subsequent years. The adoption of better systems of tapping, 

 which obviate the necessity of paring away the tissues wherein the 

 milk accumulates, and drawing supplies of latex by merely cutting 

 and not excising the laticiferous tissues, is bound to result in an 

 increased yield, since the life of the tapping area is so much 

 prolonged. The fact that a few well-developed trees have been 

 made to give as much as 12 to 25 lb. of rubber per year, and 

 promise abundant yields in the very near future, shows] what a 

 tremendous amount of material there is to draw upon, providing the 

 environs of v the plant and tapping operations are fully understood. 

 The heavy yields reported in one part of this chapter are, however, 

 from exceptional trees, and when forming an estimate of the 

 average yield over a large acreage may be neglected. 



The reader is referred to the details given in the present chap- 

 ter, showing the yields obtained from Ceylon properties during 

 1905, and those giving the yield of rubber per square foot of cortical 

 tissues removed, if he is anxious to form an estimate of the rubber 

 obtainable on an estate where the available tapping area and bark 

 thicknesses are known. 



The Effect of Repetitional Bark Stripping. 



It is common knowledge that many of the excessive yields 

 have been obtained by completely excising the whole of the bark 

 tissues from the base up to a height of six to fifteen feet, and it is 

 natural that some questions should be put forward as to the pro- 

 bable effect of such treatment on the plants. 



At the outset it must be recognized that the great function of the 

 cortical or bark tissues is to conduct the elaborated food materials 

 produced in the leaves, from above downwards, to various sections of 

 the growing plant and also to store up, in certain of its cells, a quan- 

 tity of food as reserve material. As a store house and conducting 

 channel it is of vital importance to the plant, and if it is removed too 

 quickly the life of the tree may be endangered. The internal wood, 

 though of great importance to the plant in conducting, from below 

 upwards, the water and mineral food absorbed by the roots, is less 

 vital than the cortex, and the internal portion may, to a certain extent, 

 be dispensed with without very seriously injuring the tree. The 

 cortical tissues are dependent for their renewal on the activity of the 

 cambium — a delicate tissue separating the inner cortex from the 

 wood — and in the natural course of events gradually dry up near the 

 surface and peel off in the form of dead bark. The inner cortex, 

 originally containing the latex tubes, is therefore ultimately cast off 

 as dead bark, so that it may be said that cortical stripping, in tapping 

 operations, is one way of expediting the removal of the bark tissues 

 and may be effected without seriously disturbing the execution of 

 the normal functions of the plants. 



