Gums,[Resins, 



102 



[August, 1910. 



however, show a yield per tapping nearly 

 four times as great as the first seven. 

 The point which requires explanation 

 here is the yield of group A (25 trees). 

 The yield per tapping in alternate 

 day tapping is more than double that 

 in the every day tapping ; and so 

 is the yield in the weekly tapping. 

 Even the yield in monthly tapping is 

 greater. But the yield per tapping for 

 three day tapping is quite out of the 

 series, and is even less than that for 

 daily tapping 1 The only possible explan- 

 ation would seem to be that the trees 

 of group A were not comparable with 

 those of the other groups. That it is 

 hot a question of "wound response " is 

 shown by the yield of group F. 



Dividing up the yields according to 

 the three periods as before, we obtain 

 the following, the first line giving the 

 number of tappings in each period and 

 the second the yield per tree per tapping 

 in ounces : — 



D. E. A. F, 



September- February. 



112 56 37 18 



0-88 oz. 1-49 oz. 0-88 oz. 1-52 oz. 

 February -April. 



56 27 20 10 



0-67 oz. 2-78 oz. 0'65oz, 1-29 oz. 

 April-September. 



102 53 34 16 



0'39 oz. 0-79 oz. 0'22 oz. 129oz. 



In group D there is a regular decrease 

 as tapping proceeds. In Group A there 

 is a similar decrease, but though the 

 figures for A and D are practically equal 

 in the first two periods, A shows a much 

 bigger drop in the third period, although 

 it had been tapped only one-third the 

 number of times, F shows a drop in the 

 second period, but, probably because the 

 number of tappings is small, the yield 

 per tapping in the third period does not 

 decrease further. But E, which provides 

 the conclusion of the experiment, does 

 not fall in with this series. In the first 

 period its yield is less than twice that 

 of D, but in the second period it jumps 

 to more than four times that of D, to fall 

 again to about twice in the third period. 

 If this is the result of the smaller num- 

 ber of tappings, why does it not occur 

 in group A ? If it is a result of the fact 

 that the ante " wound response" tap- 

 pings form a greater proportion of the 

 tappings of the first period in E than in 

 D, why does it not occur still more 

 markedly in F? 



Experiments 4 and 5. 

 The figures published are insufficient 

 to admit of any conclusions being formed 

 in Experiment 4, and it is doubtful 

 whether the necessary data were ever 



obtained. Experiment 5 does not seem 

 to have been carried out. 



From the foregoing it is evident that 

 deductions which have been based on 

 Experiment 1 certainly do not follow 

 from the results of that experiment ; and 

 further that although the final figures 

 of Experiments 2 and 3 support the con- 

 clusions published by Wright and Par- 

 kin, yet analysis shows that they con- 

 tain so many anomalies that they cannot 

 be relied on. The proposition? which 

 these authors assert may be quite true ; 

 but they cannot be deduced safely from 

 the Henaratgoda results. On the whole, 

 the latter give the impression that the 

 experiments were planned on so large a 

 scale that adequate control was im- 

 possible. 



THE SCIENCE AND PRACTICE OF 

 PARA RUBBER CULTIVATION: 

 THE NEW TROPICAL INDUSTRY 

 OF THE EAST. 



By John Parkin, m.a., f.l.s. 



(From Science Progress, No, 16, 

 April, 1919.) 



Yield. 



The rubber-producing capacity of 

 cultivated Heveas has in the past been 

 under-estimated, and even now the full 

 extent to which it may ultimately reach, 

 as the trees mature, cannot be said to 

 have been gauged with any degree of 

 accuracy. 



An average of one and a half pounds 

 per annum for a tree twelve years old 

 was the original calculation for Ceylon, 

 but this was before wound-response had 

 been taken into account. In Malaya six- 

 year-old plantations are now giving 10 

 oz. to 1 lb. a tree, an amount gradually 

 advancing to 3 lbs. as the trees reach an 

 age of 10 years ; higher subsequent 

 yields are expected. A few old, well- 

 developed trees have given 12 to 25 lb. 

 each per annum. Eight seventeen-year- 

 old Heveas in the Perak State, of an 

 average girth of 55 inches, have supplied 

 28| lb. of dry rubber per tree. 



The Cicely Estate, one of the older 

 Malay companies, obtained an average 

 of 6 lb. per tree from 9,000 which were 

 regularly tapped in 1908. The age of 

 these trees varied from about ten to five 

 years, but a third of them were of the 

 latter age, undergoing their first tap- 

 ping , consequently some of the older 

 trees must have yielded well over 6 lb. 

 of rubber per annum. 



