RUBBER 645 



yield of the full herring-bone, on the same area, should 

 be intermediate between the two. In searching for con- 

 firmation of this in the published experiments, one finds 

 that in the majority of cases the direction of the cuts of 

 the half herring-bone' has not been recorded, and hence 

 no valid conclusions can be drawn. A more serious defect 

 is that, in general, experiments on the problem of half 

 versus full herring-bone have been combined with experi- 

 ments on half versus quarter circumference. So far as 

 I am aware there is as yet no definite comparative experi- 

 ment, except that of Dr. de Jong, between the half and 

 the full herring-bone, or their reduced equivalents, the 

 single and the V cut. In an experiment carried out at 

 Peradeniya for twelve months in 1910, on half the circum- 

 ference in each case, the half herring-bone to the left 

 yielded more than the half herring-bone to the right, but 

 the full herring-bone yielded more than either. As, 

 however, the number of cuts was varied during the year 

 this result is inconclusive. 



An experiment on this point is decidedly wanted : I 

 mean an experiment carried on until all the available 

 tapping surface has been completed. The three patterns 

 of tappings should be compared on quarters, and also on 

 the half circumference. It would seem probable that the 

 method which is most suitable for the quarter might not 

 be most suitable for the half circumference. 



In this connection it may be as well to call attention 

 to another factor which vitiates so many of the earlier 

 experiments. It is essential that all tapping in a com- 

 parative experiment should be done at the same angle. 

 Not only does the yield per tapping vary with the angle, 

 but the number of tappings which it is possible to make 

 to the inch, measured along the channel, varies with the 

 angle also. Now, the yield from a given area of bark 

 depends to a great extent upon the number of tappings 

 it is possible to make on that area, and the number of 

 tappings depends upon the angle. The greater the angle 

 the cut makes with the vertical the greater the number 

 of tappings to the inch. Therefore, for two reasons, the 

 yield from a given area depends upon the angle of the 

 cut. 



