September, 1910.] 



195 



Saps and Exudations. 



estates is now being carried on con- 

 tinuously, and the question is whether 

 the yield is greater in tapping continu- 

 ously daily, or continuously every other 

 day.* The experiment carried out at 

 Henaratgoda in 1905-6, if taken at its 

 face value, shows that more rubber is 

 obtained by tapping every other day 

 than by tapping every day throughout 

 the year. Most people, however, do not 

 accept this. The yield per tapping in 

 alternate day tapping is greater than 

 that obtained in daily tapping, but it is 

 less than double the latter. Therefore 

 the amount obtained at the end of the 

 year by alternate day tapping should 

 be less than that obtained by daily tap- 

 ping for the same period, but greater 

 than half the latter. The experiments 

 would seem to show that it should be 

 about three-quarters. The gain is there- 

 fore in the labour per lb. of rubber ob- 

 tained ; but the greatest yield in a given 

 time is obtained by daily tapping. 



The Singapore table 5 is quoted below, 

 split into two to suit the columns of 

 the "T.A." 



Tapped Daily. 



No. of 

 Experi- 

 ment. 

 I. 

 II. 

 III. 

 IV. 

 V. 

 VI. 



No. of 



No. of 



trees 



times 



tapped. 



tapped. 



50 



105 



120 



43 



60 



20 



200 



103 



200 



80 



150 



78 



780 



429 



Dry 

 weight of 

 Rubber 

 lbs. oz. 

 217 15 

 129 12 

 25 2| 

 673 



453 8| 

 680 7 



2,180 7 



4 



No. of 

 Experi 

 ment. 

 I. 

 II. 

 III. 

 IV. 

 V. 

 VI. 



Tapped Alternate Days. 



Dry 



No, of No. of weight of 

 trees times Rubber 

 tapped, tapped, lbs. oz. 



120 

 140 

 120 

 200 

 150 



730 



67 

 63 

 18 

 15 

 51 



308 3| 



264 3| 



99 7i 



195 8* 



187 9| 



214 1,055 0| 



The table is followed by a calculation 

 that if 730 trees tapped on alternate days 

 214 times yield 1,055 lbs. of rubber, then 

 780 trees tapped on alternate days 429 

 times will yield 2,261 lbs. of rubber. 



* As these and other similar experiments are 

 designed merely to show the relative yields, any 

 discussion of the effect of either system on the 

 tree is irrelevant. 



There is therefore a gain of 81 lbs. in 

 favour of alternate day tapping. But 

 this is only arithmetic, not rubber 

 tapping, for the trees do not obey the 

 rules of simple proportion, and they 

 would not go on yielding at the same 

 rate if the numbers of tappings were 

 doubled. 



Moreover, the arithmetic is incorrect, 

 It is not correct to add the numbers of 

 trees together, and the numbers of 

 tappings, and to argue that 730 trees 

 were tapped 214 times, or that 780 trees 

 were tapped 429 times. If the ordinary 

 Rule of Three is to be adopted, the 

 numbers of tappings must be averaged 

 by the usual principle of " proportional 

 parts." Worked out correctly, the daily 

 tappings are equivalent to 780 trees 

 tapped 77 times (76*8), while the alternate 

 day tappings are equivalent to 730 trees 

 tapped 41 times (40'6), or 780 trees tapped 

 38 times. From this it may be calculated 

 that if 780 trees tapped 38 times on 

 alternate days yield 1,055 lbs. of rubber, 

 then if tapped 77 times (76*8) on alternate 

 days they would yield 2,132 lbs. Compar- 

 ing this with the yield obtained in daily 

 tapping, we find tliat the alternate day 

 tapping, even when calculated instead 

 of being actually obtained, shows a loss 

 of 48 lbs. The gain of 81 lbs. given in 

 the Straits Bulletin is due merely to 

 incorrect arithmetic. 



This result is so contrary to expect- 

 ation that it is necessary to enquire 

 further into the figures. If we calculate 

 the yield per tree per tapping in ounces, 

 we obtain the following results :— 



No. of 



Daily 



Alternate day 



Expt. 



tapping. 



tapping. 



I. 



0-66 





II. 



0-40 



0-61 



III. 



0-335 



0-48 



IV. 



0-52 



0-74 



V. 



0-45 



1-0 



VI. 



0-93 



0-39 



Experiment II. is in accordance with 

 expectation ; the amount obtained per 

 tapping in alternate day tapping is about 

 50 per cent, greater than that obtained 

 in daily tapping. Experiments III. and 



IV. agree with this. But Experiments 



V. and VI. do not. Experiment V. shows 

 a yield per tapping more than twice as 

 great as that obtained in daily tapping, 

 while in Experiment VI. the difference is 

 completely the other way. 



When numbers disagree in this way, 

 it is always advisable to look for errors, 

 and if we turn to the detailed results of 

 Experiment V., we find that the trees in 

 alternate day tapping were not tapped 



