August, 1910.] 



99 



Saps and Exudations. 



(2) " The full spiral, of all methods of 

 tapping, yields the largest quantity of 

 rubber in a given time." 



(3) "The experience of planters and 

 others has since shown that two days is, 

 as a rule, the best interval between 

 successive tappings, but some estates 

 tap every day with good returns." 



It must be remembered that the 

 Henaratgoda trees differ considerably in 

 age and size. For" the purpose of these 

 experiments they were divided into 

 groups ; and we must assume that they 

 were grouped in such a way that the 

 groups of one experiment were composed 

 of trees approximately equal in size. It 

 would have been of value if the girths of 

 the trees had been stated, but this detail 

 is omitted. Further, the trees of the 

 different experiments were tapped at 

 different times and by different methods, 

 It is impossible, therefore, to draw any 

 valid conclusions by selecting for com- 

 parison groups of trees which formed part 

 of different experiments. We are restrict- 

 ed to the trees which were originally 

 selected as comparable, and which were 

 tapped in the same way or at the same 

 time. It is only by ignoring this pre- 

 caution that Parkin can arrive at the 

 first result quoted. 



Experiment I. 

 To Determine the Yield of Rubber 

 prom Different Parts of the Stem. 

 Wright's deduction from this experi- 

 ment is identical with Parkin's. But it 

 is formed on figures which only deal with 

 from one-third to one-tenth of the total 

 tappings. The total number of tappings 

 in the various groups which were experi- 

 mented upon were 92, 95, 94, 94, 93, and 84. 

 Yet Wright's conclusions are based on 39, 

 16, 16, 16, 23, and 8 tappings respectively. 

 Even then the yields for those tappings 

 do not support his conclusions, and he 

 only obtains his results by calculating 

 the yield per unit of bark excised. This 

 method of calculation is quite fallacious, 

 since it assumes that the quantity of 

 rubber obtained is proportional to the 

 area of bark excised. The fallacy is 

 widespread, and calculations of yields 

 have recently been published which 

 were obtained by tapping a small 

 area of bark, and multiplying the 

 result by the number representing the 

 ratio of the total area of the stem to 

 the area of bark tapped! It only 

 requires a slight consideration to show 

 that this method is wrong. If cooly A 

 cuts off a strip one-sixth of an inch 

 broad, in the same time that cooly B 

 cuts off only one-twelfth of an inch, A 

 does not get twice as much rubber as B. 

 If, however, A cuts off his sixth in two 

 days' tapping, he may get twice the 



amount that B obtains by cutting off 

 his twelfth in one day's tapping. Thus 

 the amount of bark excised is no 

 standard by which to estimate the yield, 

 except in so far as it indicates the dura- 

 tion of the tapping period. To make 

 the bark last as long as possible is a 

 sound principle, but to calculate yields 

 per unit of bark excised when the 

 strips excised per tapping vary in 

 breadth from one-sixteenth to one- 

 quarter of an inch is merely juggling 

 with figures. 



The trees of this experiment were all 

 tapped by the full herring bone with 

 cuts 1 ft. apart. They consisted of the 

 following groups : — 



No. of trees. Tapped from 



C. ... 25 . . base to 5 ft. 6" 



M. ... 2 ... 6 „16„ 



N. ... 2 ... 10 „20,, 



O. ... 2 ... 20 „ 30 „ 



L. ... 1 ... base ,, 30 ,, 



W. ... 2 ... „50„ 

 The final results are as follows :— 



C. M. N, O. L. W. 



Number of tappings. 

 92. 95. 94. 94. 93, 84. 

 YTield per tree in lbs. 

 3 8'7 12-2 8-7 14'5 15. 

 Tapping the basal 5 feet 6" gives 3 lbs. 

 of rubber per tree ; with less than twice 

 the length of trunk, 6-16 ft., the yield is 

 nearly three times as great, and the 

 same is true for the length, 20-30 ft. ; 

 from 10-20 ft., less than twice the length 

 tapped in group C, the yield is more 

 than four times as great. Only in the 

 last two groups is there any falling off. 

 When the length tapped is increased 

 about 5£ times, the yield is less than 

 5 fold, and when the length is increased 

 nine times, the yield is only 5-fold. But 

 in the last case the tappings are fewer. 

 These results certainly do not bring out 

 the superior producing capacity of the 

 basal 6 ft. 



The figures given in the pages of the 

 " T.A-," the Annual Reports, etc., enable 

 us to divide up the experiments into 

 three periods, viz., September, 1905, to 

 February, 1906, February, 1906, to April, 

 1906, and April, 1906, to September, 1906. 

 From this we find that while C was tap- 

 ped fairly regularly, twice per week, the 

 remaining groups were tapped at odd 

 intervals. Thus we have the following 

 numbers of tappings :— 



C, M. N. O. L. W. 



First tapping period. 

 39 16 16 16 23 8 



Second tapping period. 

 18 29 28 28 24 29 



Third tapping period. 

 35 50 50 50 46 47 



