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'Vhe Supplement to the Tropical Agrtculturxst 



of bark or by removal of latex. U is usual to 

 discuss only the former kind of loss in this con- 

 nection, but a tree can undoubtedly be over- 

 tapped by pricking only, without any removal of 

 bark. In many systems of pricking the damage 

 to the bark is at least as great as in the case of 

 pariug, and with the best possible pricking 

 some damage is inevitable. Removal of latex 

 without damage to the bark is in fact impos- 

 sible, but, even if it were possible, there can be 

 no doubt that there must be a limit to the 

 quantity of latex which could be extracted 

 without damage to the tree. The manufacture 

 of latex necessarily uses up a certain amount of 

 food and energy, and the supply of them in the 

 tree is not unlimited. This is, of course, assum- 

 ing that latex is not exclusively a waste product. 

 The problem of the physiological effect of paring 

 upon the tree is, therefore, a complicated one. 

 Besides the rate of removal of bark, the amount 

 of latex taken from the tree and the frequency 

 of its removal has to be considered. The 

 real problem relates to the frequency of re- 

 moval, but it is quite impossible to die- 

 sociate this effect entirely from the damage 

 done by bark removal and the drain upon the 

 resources of the tret> entailed by latex removal. 



In the present experiment some of the trees 

 may be said to have been overtapped, because 

 the whole of the outer bark has been removed 

 up to the greatest height convenient for tap- 

 ping, and renewal of the first and second areas 

 tapped is still imperfect. The result is probably 

 due, at least in part, to the use of the pricker, 

 and the bark might have shown perfect renewal 

 if the method of paring only had been employed 

 from the outset.* In any case it is necessary to 

 rest the trees from the /point of view of bark 

 renewal only. The two rows (1 and 11) have 

 yielded at the rate of 770 and 650 lb. of dry rub- 

 ber per acre annually for four years, which 

 seems to be quite as much as one has any right 

 to expect from close-plant * J fcroes in poor soil, 

 whatever their age may be. Assummg a sys- 

 tem by which the whole outer bark to a certain 

 height is removed, a tree will certainly have 

 been overtapped, says the bulletin, if the renewed 

 bark is found not to be ready for tapping when 

 the time previously assigned for such tapping 

 comes round. From the evidence of the pre- 

 sent experiment Dr. Lock and Mr. Bamber are 

 inclined to extend the idea of overtapping 



*In the case of large wounds, caused by the 

 death of the pricked bark, complete healing may 

 be delayed for many years. Such damage should 

 be distinguished from simple overtapping, 

 ^-Bulletin, 



somewhat further, and to asseTt that a tree may 

 be overtapped although there is still a con- 

 siderable area of original bark available for 

 tapping. Thus, from the evidence alone they 

 are disposed to draw the conclusion that 

 one of the rows (III) was being tapped too 

 rapidly, since the yield from the second of two 

 similar areas is materially less than that from 

 the first. From thi3 point of view the tapping 

 (even of row IV.) seems to be unsatisfactory, 

 and a proper rate of tapping on the system 

 employed is reached first in the case of 

 row V. In the case of young and growing 

 trees, planted with plenty of space, the 

 authors of the experiment think that over- 

 tapping was taking place unless the second 

 of two similar areas yielded decidedly more 

 than the first. It is probable that the over- 

 tapping of row HI. is associated with the 

 poverty of the trees and their crowded condi- 

 tion, for the interval allowed for renewal in this 

 case is between 5 and 6 years, a period which 

 would undoubtedly be ample for trees which 

 were widely spaced. Experience seems to shew 

 that young and vigorous trees can be tapped at 

 a rate which exhausts the available bark in four 

 years, at the same time making good growth 

 and giving a steadily increasing yield. At the 

 end of the four years the first area tapped 

 should be again ready for tapping. The results 

 here obtained are regarded as a warning that 

 there are strict limits to the recuperative 

 powers even of Hevea. In fact, the Hena- 

 ratgoda experiments may be said to endorse 

 the view that, even in the case of the most 

 vigorous trees, the period allowed for the first 

 renewal should not be reduced below four 

 years. The important point, however, is that, 

 with light tapping steadily continued at inter- 

 vals of from five to nine days, trees, although 

 old and very closely planted, can be educated to 

 give a greatly increased yield per tapping. The 

 conclusions come to are as follows : — 1. When 

 Hevea rubber trees were tapped at different 

 intervals on the system here described, the 

 yield per tapping increased with the increase of 

 interval up to an interval of about a week be- 

 tween successive tappings. 2. The yield for a 

 given period was greatest at first from the trees 

 tapped at frequent intervals. The relative yield 

 from the trees tapped at longer intervals gra- 

 dually increased until, after three and a half 

 years' continuous tapping, the yield from trees 

 tapped once a week may, at a particular season, 

 become as great or greater than that from trees 

 tapped at any shorter interval. 3. This conclu- 

 sion is at present confined to the case of a parti- 

 cular plantation of trees, upwards of twenty 

 years old, planted at a distance of only twelve 

 by twelve feet. 



