886 



[May, 1912. 



On the second point criticized we are definitely in disagreement with the 

 Editor of the India Rubber Journal. The statement complained of is that the 

 interval between successive tappings, provided that it does not exceed a week or so, 

 makes little difference to the yield of rubber per tapping. Our most recent results 

 necessitate a modification of this statement, but not in the direction indicated by 

 the India Rubber Journal. Although we feel certain that this is not his real 

 opinion, the further remarks of the Editor suggest that he is in agreement with the 

 view we once heard expressed by a young Superintendent, namely, that it was desir- 

 able at all costs to get through the bark marked out for a specified period. A more 

 wrong-headed view than this could not possibly be taken, and we do not seriously 

 attribute it to the India Rubber Journal. 



As a matter of fact, the interval between successive tappings does make a dif- 

 ference to the yield of rubber per tapping. And the difference is in favour of an 

 increased interval between successive tappings — not a reduced one. The difference 

 appears to become greater, the longer the trees are tapped, and we have only 

 arrived definitely at the opinion stated after nearly four years of continuous 

 experiment. In support of this statement the following fact3 are sub- 

 mitted. For a full account of the Experiment down to the end of February, 1911, 

 the reader is referred to Circulars 9 and 18 of Vol. V., obtainable from the 

 Botanic Department. The further account of this experiment is likely to be 

 considerably delayed owing to stress of work. We, therefore, take this opportun- 

 ity of making public one of the most important results attained. 



The experiment described was carried out on seven rows of ten trees each. 

 The trees are old and closely planted. The rows are numbered I. to VII. and 

 tapping was carried out, on the system described in the Circulars, in the same 

 way on all the trees except that the interval between successive tappings was 

 different for the different rows. The following table shows the average interval 

 in days between successive tappings and the number of years allowed for renewal 

 on the system adopted :— 



I. II. III. IV. V. VI. VII. 

 Interval ... 1*4 2-6 3-9 5-1 6-5 7'8 9'0 days. 



Period of renewal... 2'3 4 6 7 8 9 10 years. 



The average yield per tapping of ten trees is given in grammes in the fol- 

 lowing table, which covers the last six months of 1908 and whole of 1909-10-11. 

 During the whole of this time the experiment was carried on without a break. 



Average Yield per Tapping. 







I, 



II. 



III. 



IV, 



V. 



VI. 



VII. 



1908 





100 



107 



148 



158 



169 



210 



163 



1909 





57 



72 



86 



91 



113 



121 



108 



1910 





58 



69 



67 



96 



118 



115 



115 



1911 







87 



78 



143 



169 



176 



154 



One of the best yielding trees in row III. had unfortunately to be cut out 

 early in 1910 owing to canker. No allowance is made for this fact in the above 

 table, but in the table which follows one-fifth of the actual yield is added to the 

 yield for row III. 



It was obvious early in 1910 that some of the weaker trees of row I. had 

 suffered from the rate at which they had been tapped, and it was not thought 

 desirable to continue operations on the renewed bark. 



Now it might be thought possible to draw the conclusion at once from the 

 above table that the yield of rubber per tapping increases directly with the inter- 



