RUBBER PLANTING 61 



It will be seen that after 14 tappings made at inter- 

 vals varying from three to seven days (average interval 

 5 -6 days), the yield had increased by over 600 per cent. 

 The increased yield thus recorded was ascribed to the 

 effect of wound response. 



There seems to be little doubt that the increase 

 recorded by Parkin was an exceptional one, and that 

 rather too much weight has been laid on the phenomena 

 observed. It is quite possible that part of the increase 

 was due to climatic conditions, and this view is sup- 

 ported by the -rainfall returns during the period of the 

 experiment, which have fortunately been preserved. 

 They are as follows: 



TABLE IX 

 Rainfall at Peradeniya y 1899. 



Inches 



March 5-42 



April 18-40 



Inches 

 May 7-59 



June 1074 



Reasons for the increase of yield on tapping. 



It is possible that the immediate response to tapping 

 is partly due to a reduction in the viscosity of the latex, 

 which is thus enabled to flow more freely. When part of 

 the latex is removed from the vessels by tapping, the in- 

 ternal pressure of the latter is reduced and the remaining 

 latex is diluted by the entrance of sap from the surround- 

 ing cells. The pressure in the surrounding cells may 

 also be increased owing to the irritation consequent upon 



