260 



[Sept. mm 



Correspondence. 



RUBBER TAPPING METHODS. 



A COMPARISON OF THE SPIRAL, HALF-SPIRAL, AND HERRING-BONE METHODS. 



Sir,—" One cannot have omelettes without breaking eggs." There is an 

 egg that wants breaking badly ; and I trust the omelette will not prove indiges- 

 tible ! I refer to the mystery which enshrouds the question of " The Unit of Bark 

 to Yield of Rubber." 



Many rubber planters, even among those who no longer hold the crude 

 idea that full spiral tapping, even when carefully done, is a species of ringing the 

 tree, still hesitate to adopt this method, obviously the easiest and cheapest of the 

 three, because the dictum has gone forth, with good authority, that the Peradeniya 

 and Henaratgoda experiments prove that the greatest yield per unit of bark 

 excised has been given by the herring-bone system, though the greatest yield psr 

 tree has been given by the full spiral. They, therefore, imagine that there is a 

 desideratum in herring-bone tapping, in spite of all its disabilities of left, as well as 

 right, hand cutting, of many drip-tins or expensive manual application of water to 

 the various cuts, and of untappable areas which is not to be found in spiral tapping ; 

 and that while prices rule high, the extra expense of these disabilities will be 

 more than covered by the bark lasting longer. 



It is my purpose to show where the fallacy has crept in, unavoidable and 

 accidental though it be. 



As it is an accepted fact that the latex cells lie in series in the 

 line of the stem, and that the greater and freer drainage and inter-drainage 

 of these series of cells takes place in that line, it follows that many 

 more cells will be drained by a cut across that line than by one in its 

 length ; in effect that a level cut across the bark gives the greatest 

 possible yield of latex and the perpendicular cut the least— the cuts being of 

 equal length. We also know that these cells, after drainage, have the power of 

 sealing themselves up and again becoming full of latex in about two days, when a 

 thin paring cut will re-open them and give another full flow ; and so on while the 

 bark lasts. Now, in the case of the perpendicular cut a whole series of cells is 

 entirely removed which would otherwise have filled up again with latex ; whereas 

 in the level cut only the ends of the series are removed, and the same area of cells is 

 drained over and over again. It, therefore, follows that : —(1) the nearer the level 

 the cut is made, the greater the yield and the less the excision of bark ; (2) the nearer 

 the perpendicular the less the flow and the greater the excision of bark. And 

 since we have the choice of any angle between level and perpendicular, or zero and 

 90°, it follows that the man who taps at an angle of 75% 80° or 85°, is little 

 better off in yield and loss of bark than the man who taps perpendicularly. 

 While he who taps at 20°, 15°, or 10°, has nearly as good a return as the level tapper. 

 But these low augles suffer from the disability that latex will not run in chanuels 

 on such gradients and so becomes scrap, which for cogent reasons does not suit the 

 practical planter. He, therefore, sets about to find the lowest angle at which 

 natural latex would flow, and by some strange fate 45° was fixed on for the spiral 

 method especially. (I suppose because it was so easily made by cutting a square 

 sheet of tin diagonally across and using each half as a guide for his line on the tree.) 

 But there it has stuck — at 45' ! ! Even in the Botanic Gardens mentioned above, no 

 other angle than 45° for the spiral has been used, to the best of my knowledge ; and 

 certainly no other augle on the various estates I have visited. For the herring-bone, 

 on the other hand, both in the Botanic Gardens and on these estates, exceedingly flat 

 angles have entirely been used, in some instances so flat and irregular that the latex 

 had to be coaxed into the runnel by au attendant who could look after only a few 

 trees at a time. 



