Gums, Resins* 



292 



[April, 1912. 



different trees according to their size 

 would doubtless lead to difficulties in 

 estate work, and under these circum- 

 stances we should recommend an interval 

 of four years rather than one of three, 

 except under very favourable conditions. 



As regards the size at which tapping 

 may safely be begun, we consider that 

 trees less than five years old from plant- 

 ing should not be tapped at any point 

 where they are less than 18 inches in 

 girth. The reason for this restriction is 

 that the bark is then so thin that it is 

 almost impossible to pare without caus- 

 ing injury to the tree. 



If it is decided to allow four years for 

 the renewal of the bark, the simplest 

 system which can be adopted is to divide 

 the circurnfeience of the cree into four 

 equal parts, and to tap these successively 

 by the half-herring-bone method. Each 

 quarter section of the tree will then 

 represent a year's tapping. The quarter 

 section opposite the first should be 

 tapped second, and the other two in 

 order. 



Tapping at Various Levels. 



In an experiment at Henaratgoda 

 twenty-nine trees were tapped daily by 

 the herring-bone method with six cuts 

 placed at vertical intervals of a foot. 

 During the first month's tapping the 

 three upper cuts yielded together a daily 

 average of 558 cc of latex (nearly a pint), 

 and the three lower cuts a daily average 

 of 561 cc. During the last month, at the 

 end of which the bark between the cuts 

 had been almost entirely removed, the 

 average daily yield from each of the six 

 cuts was as follows : — 



1. 2. 3. 4. 5. 6. 

 77 86 98 82 83 440 



Thus, when the bark between the cuts 

 is nearly exhausted, the lowest cut yields 

 as much latex as all the other five put 

 together. In addition, the latex from 

 the lowest cut is more concentrated, and 

 contains a higher percentage of rubber. 



These were old trees with a good thick- 

 ness of bark. In the case of youns trees 

 we should expect the difference to be 

 gven greater. 



A Criticism. 

 While we admit that the vigour of the 

 tree must be taken into account in deter- 

 mining the renewal of the bark, we can- 

 not understand upon what evidence 

 tapping renewed bark three years old is 

 recommended. We have experience in 

 many countries and on trees of different 

 agesi and our view is that the four years' 

 interval for bark renewal which we have 

 laid down, should only under very excep- 

 tional circumstances be reduced. We 

 would rather see the interval allowed 

 for renewal of secondary bark increased 

 to even five years than reduced to 

 three. We are aware when making 

 this statement that many trees upon 

 which tapping was commenced when 

 they were three years old appear to 

 grow so vigorously that the renewed 

 bark presents the general characters of 

 primary bark when under four years 

 old, and that on many estates such bark 

 has been tapped and good yields obtained. 

 But we also have information to hand 

 which teaches us that even with a four 

 years' bark renewal there is a check to 

 the average growth of the tree, and that 

 the yield of the rubber from renewed 

 bark is not so much as many have been 

 led to expect. We are informed that a 

 gentleman who hails from Johore, and 

 whose experience over a very large area 

 of tappable trees is well-known, prefers 

 to increase not only the period of the 

 bark renewal above four years, but also 

 to increase the minimum size of tapping 

 from eighteen to twenty inches a yard 

 from the ground. We believe it to be a 

 much wiser course to adopt a method 

 which will relieve to some extent the 

 strain on the trees which the removal 

 of the bark undoubtedly involves ; it is 

 better to aim at a long life and good 

 steady yields rather than high yield 

 and premature death. Until we see 

 more evidence against us we shall con* 

 tinue to recommend a minimum period 

 of four years for bark renewal in even 

 the favoured countries, and a much 

 longer interval for trees at high ele- 

 vations, on bad soils, or in unsuitable 

 climates. 



