RUBBER PLANTING 137 



injury to the tree. Some authorities would increase 

 the minimum size allowed to a girth of 20 inches or 

 more. 



If it is decided to allow four years for the renewal 

 of the bark, the simplest system which can be adopted 

 is to divide the circumference of the tree into four equal 

 parts, and to tap these successively by the half-herring- 

 bone method. Each quarter section of the tree will 

 then represent a year's tapping. The quarter section 

 opposite the first should be tapped second, and then the 

 other two sections successively, in order to preserve the 

 symmetry of the tree as far as possible. 



Systems of Paring. 



The system of tapping adopted in the experiments 

 described in Chapter IV was one of superimposed Vs. 

 The cuts were made at an angle of 45 degrees with the 

 horizon, and the vertical distance between successive 

 cuts was one foot. In describing other systems we may 

 assume for the present a similar angle of cut, and a 

 similar distance between successive cuts where there are 

 more than one. The half-herring-bone system (Fig. 16) 

 referred to in the last paragraph consists of a vertical 

 conducting channel into which a single series of slanting 

 cuts leads on one side only. Such a system may be 

 derived from the superimposed V system by obliterating 

 one limb of each V. Reasons have already been given 

 for confining such a system to one quarter of the 



