648 RUBBER 



as yet, no experiments on tapping one side continuously 

 versus tapping two opposite sides alternately. 



As already intimated, the yield per tapping in alternate 

 day (two day) tapping is greater than the yield per 

 tapping in daily tapping. But it is not twice as great. 

 Hence the yield in a given time is greatest with the 

 shorter interval. Alternate day tapping usually yields 

 from 20 to 30 per cent, more per tapping than daily 

 tapping. The yield at the end of a year in alternate day 

 tapping is therefore not more than 65 per cent, of that 

 obtained by daily tapping, but the amount of bark con- 

 sumed is only about one-half. Alternate day tapping 

 gives about 20 to 30 per cent, more rubber than daily 

 tapping from the same area of bark, but it takes twice 

 the tjme to do it. 



Some doubt has been thrown on the above results by 

 the experiments which have been in progress for six 

 years on the old trees at Henaratgoda. In these experi- 

 ments, in which the interval varies from one to seven 

 days, the results at first were in accordance with the 

 statements of the last paragraph. But after four years' 

 continuous tapping the yield of the trees tapped at the 

 longer intervals increased to such an extent that not 

 only was the yield per tapping greater than with the 

 shorter interval, but also the yield in a given time. 



This result has been attributed to the fact that the 

 trees are old and closely planted, and that consequently 

 the trees tapped daily are overtapped. It will be neces- 

 sary, therefore, to repeat the experiment with younger 

 trees and a more conservative method of tapping. One 

 such experiment is already in progress at Peradeniya. 



It may be noted that tapping every three days has been 

 practised in Ceylon, on at least one estate, for several 

 years. 



Many experiments give variants of interval experi- 

 ments, or combinations of the interval factor with one 

 other. Probably the most common is the experiment 

 which combines daily versus alternate day tapping with 

 the condition that the consumption of bark is to be the 

 same in the two cases. This, of course, involves the 

 use of twice as many cuts in the alternate day tapping. 



