642 RUBBER 



criticism that his tapping problem is " purely academic. " 

 Our knowledge of rubber tapping would have been in a 

 far more advanced stage to-day had experiment stations 

 and botanic gardens restricted their tapping experiments 

 to " purely academic " problems during the last ten years. 



The first attempt to ascertain the fundamental principles 

 of Hevea tapping was made by Parkin in Ceylon in 1898. 

 He dealt with single incision methods only, i.e., either 

 single oblique cuts, or single small V's arranged more 

 or less regularly over the lowest 6 ft. of the stem. He 

 was followed by Arden, who carried out further experi- 

 ments in the Federated Malay States in 1901-02. Arden 

 also worked chiefly with single incision methods, but in 

 some experiments he adopted the "excision" method, 

 limiting the reopenings of the cut, however, to fourteen. 



The ideas obtained from Parkin's and Arden's experi- 

 ments have practically governed Hevea tapping until 

 quite recently, though it is clear that they were founded 

 on quite a different style of tapping from that in vogue. 

 Dr. A. W. K. de Jong has recently carried out more 

 exact experiments in Java on some of the questions dealt 

 with by Parkin and Arden, as well as on other points, 

 by modern methods of tapping, and his Bulletin (Hevea 

 brasiliensis, Wetenschappelijke Proeven, Buitenzorg, 

 1913) now supplies a scientific foundation. His experi- 

 ments were carried on, as a rule, for a period of eight 

 months. Herein lies a possible source of error in some 

 cases, for, at the risk of seeming unduly critical, one 

 must at present insist that comparative tapping experi- 

 ments should, with few exceptions, be carried on until 

 the available tapping area has been completely tapped. 



Among the points established by Dr. de Jong are the 

 following : 



(1) As a rule a cut of a given length and direction 

 gives the same yield, if made at the same height on the 

 tree, on whatever side it may be placed. 



(2) Two equal cuts yield more than a single cut equal 

 to their combined length, the slope and height from the 

 ground being the same. 



(3) Cuts to the left yield more than equal and equally 



