April, 19i2.} 



291 



Sapa and Exudations. 



and he had formed the opinion that they 

 were only in an experimental stage. He 

 was perfectly right, and he would have 

 hardly been wrong if he had said that 

 in these things science is only appproach- 

 ing the experimental stage. 



"This should be notorious. There is 

 nothing to extenuate. To affect other- 

 wise would be unworthy of the dignity 

 of science." 



We suggest that those who profess 

 that science is already able to cure all 

 the ills that cultivated plants are heir 

 to, ought to incur the suspicion of the 

 public and of public authorities. They 



lay themselves open to a charge either 

 of ignorance or of insincerity, 



We have, perhaps, emphasized suffici- 

 ently the present imperf ection of 

 scientific knowledge. We may close 

 our remarks in a different key. The 

 future is rosy with hope. If existing 

 knowledge is limited, the course of 

 future discovery possesses no such defin- 

 able limitations. Given time, training, 

 and ingenuity in devising new methods 

 of attack upon outstanding problems, 

 our knowledge of scientific agriculture 

 cannot fail to progress steadily and 

 surely. In agriculture, no less than in 

 other lines of research, past successes 

 augur well for future progress. 



GUMS, RESINS, SAPS AND EXUDATIONS. 



NOTES ON TAPPING. 



(Prom the India Rubber Journal, Vol. 

 XLIIL, No. 8, February 24th, 1912.) 

 The Peradeniya Circular, by Dr. R. H. 

 Lock, on tapping of Hevea trees by the 

 method of paring, : though dated October, 

 1911, has only just been received. We 

 would suggest that -the staff at Pera- 

 deniya despatch their Circulars to Europe 

 more promptly. The contents of the 

 Circular are, however, of some import- 

 ance, and we propose to give publicity 

 to the views therein expressed, because 

 they are not in exact accordance with 

 those we hold. The following are ex- 

 tracts from Dr. Lock's Circular :— 



Practical Rubber Tapping. 

 Experiments carried out at Heuarat 

 goda and elsewhere have shown that the 

 interval between successive tappings— so 

 long as this does not exceed a week or 

 so— makes little difference to the yield of 

 rubber per tapping. The interval chosen 

 ie therefore mainly a matter of conve- 

 nience, and the most convenient interval 

 is usually found to be one of two days. 

 Daily tapping carried on continuously, 

 unless the area tapped is very limited, 

 entails using up the bark so rapidly that 

 all the readily accessible bark is stripped 



from the tree before the sections first 

 tapped have sufficiently renewed to allow 

 of a repetition of the process. This 

 generally means in addition an excessive 

 drain upon the resources of the tree, and 

 in this way the renewal of the bark may 

 actually be hindered. Two days between 

 successive tappings is therefore the 

 interval most commonly allowed. 



Renewal of Bark. 



The time which must be allowed for 

 the renewal of the bark differs according 

 to the size and vigour of the tree. But 

 we think that experienced planters would 

 generally agree with the following state 

 ment. If the system of tapping is such 

 as to remove the whole of the external 

 cortex to a height of 6 feet, tapping of 

 the renewed bark may be begun after 

 three years on large and vigorous trees, 

 and these may be roughly defined as 

 trees which have reached a girth of 3 

 feet at 3 feet from the ground at the 

 period in question. 



In the case of trees which do not exceed 

 2 feet in girth after two years' tapping, 

 the rate of removal of the bark should 

 bo retarded in order that the renewed 

 bark should not be touched for two years 

 more, i.e., four years in all To treati 



