- 12 - 



with lines which indicate the direction of the fibres in the stem. 

 Twenty-five Hevea sterns of various sizes which liappened to be 

 lying in my laboratory were examined ; and it was found that 

 the fibres 'sloped slightly op to the light in eighteen of thera, 

 while in the other seven they were practically vertical. The 

 latter sterns were nearly all nine inches or less in girth, while 

 the former included sterns from nine to twenty-seven inches in 

 girth. It would appear, therefore, that the slope occurs in old 

 trees, but not in very young trees. The medullary rays are 

 inclined in the same direction as the wood fibres, and as the 

 general direction of the latex vessels is governed by that of the 

 medullary rays (since they curve round the latter), it would 

 seem to follow that the latex vessels must also slope up to the 

 right. In that case it would naturally happen that tapping to 

 the left would yield more rubber than tapping to the right, 

 since the tapping cut in the former direction would sever more 

 latex vessels. For example, if the latex vessels are inclined to 

 the right at an angle of five degrees with the vertical, and the 

 cuts are made at an angle of forty-five degrees to the vertical, 

 then the cut w^hich slopes up to the left will sever nearly 

 twenty per cent more latex vessels than that which slopes up 

 to the right. 



If the slope does not occur until the trees are old, the 

 confiict of opinion on this subject might possibly be explained 

 by supposing that different experimenters had tapped trees of 

 different ages. It may of course happen that in some trees the 

 fibres are always practically vertical, an<l it is also conceivable 

 that they may slope up to the right in some trees and up to 

 the left in others, as in the coconut i)alm. 



As far as our present knowledge enables us to judge, 

 tapping to the feft should yield more rubber than tapping J:o 

 thü right. But if further oxamination should prove that right- 

 and lefthanded trees occui' at random, no diff"erence in yield 

 could be expected. 



Wiight schrijft in zijn wcik over Hevea brasiliensis (1912 

 blz. 205): 



„A series of experiments was made on trees at Peradeniya, 

 some being tapped with the cuts sloping from right to lelt and 

 others from left to right, both on the half-spiral system. 



