RUBBER PLANTING 71 



Seasonal variation. 



Some idea of the variations in the flow of latex at 

 different times of year on the Western side of Ceylon 

 may be obtained from the following table, which em- 

 bodies the results of three years' continuous tapping 

 of the 70 trees already described as having been tapped 

 at different intervals by groups of ten. Tapping was 

 carried out during the last seven months of 1908, so that 

 by the beginning of 1909 the trees may be supposed to 

 have been responding freely to the influence of tapping. 

 By taking the average of three years we can eliminate 

 to some extent the effect of different stages of tapping. 

 This is necessary because, at least when the tapping 

 intervals are short, the yield is greatest soon after a 

 particular area is begun, and falls off when the bark on 

 that area is becoming exhausted. Row I is omitted 

 because it was only tapped for a few months during 191 1. 



TABLE XIV 

 Average yields per tapping, 1909 1911 (grammes). 



