Plant Sanitation. 



[June, 1909. 



the area in the immediate neighbour- 

 hood of the wound is drained. When 

 left for a day or two the latex vessRls 

 are recharged, partly by the flow of 

 latex from other parts of the bark, and 

 partly by water from the wood. When 

 the wound is reopened by a new cut 

 which removes the plugged ends of the 

 old latex vessels, this fresh supply flows 

 out, and the process may be repeated 

 until the tree "sulks," that is, until the 

 bark has been drained as much as is pos- 

 sible through thatparticular wound. Any 

 new formation of rubber during tapping, 

 i.e., of rubber which was not in the 

 bark, at the beginning of tapping oper- 

 ations, depends on the formation of 

 new latex vessels, together with new 

 bark at the cambium ; and the amount 

 of this depends upon the length of 

 the tapping period. This addition of 

 new layers to the inner side of the bark 

 is always in progress, as far as we know 

 at present, though if the tree has a 

 season in which the stem does not 

 increase in diameter, the latex formation 

 may be expected to be in abeyance 

 then. Daring a short tapping period, 

 this new formation of latex is negligible. 

 It is important to realise that latex 

 can only be formed in the stem when 

 new tissues are being made by the 

 cambium. To fix our ideas, take the case 

 of the strip of bark round the tapping 

 cut, say a strip six inches long and four 

 inches wide. Such a strip is drained by 

 the first few tappings, and any farther 

 latex obtained from it is the result of the 

 inflow from other regions. Whether it 

 is tapped with a knife or with a pricker 

 makes no difference whatever to the 

 amount of rubber which originates in 

 that strip of bark, i.e., whether it is 

 gradually cut away or left in situ, for 

 the amount formed at the cambium 

 during the tapping period is too small 

 to affect the question. Moreover, the 

 a mount of rubber obtainable by draining 

 the tree at any given time (if total 

 extraction were possible) is a fixed quan- 

 tity, and cannot be increased except 

 by increased growth. On these consider- 

 ations it would appear that, given the 

 same area of bark to operate on, neither 

 method has any advantage over the 

 other with regard to the quantity of 

 rubber obtained. The disadvantage of 

 increasing the area horizontally has 

 already been pointed out. One dis- 

 advantage of using the pricker only 

 may be foreseen. If the pricked bark 

 does not scale off, it will be admitted 

 that the amount of new bark formed 

 behind the pricked surface will be less 

 than the amount formed on a pared sur- 

 face. Now, on the assumption that rub- 

 ber is a waste product, which scarcely 

 admits of doubt, the amount formed 



will be in proportion to the amount of 

 new bark formed, and therefore the re- 

 newed piicked surface should contain 

 less than the renewed pared surface of 

 the same age. 



The main points to be demanded of an 

 ideal tapping system are, not that it 

 should give the greatest amount of 

 rubber per unit of bark excised, but (I) 

 that it should interfere as little as pos- 

 sible with the normal growth of the tree, 

 (2) it should produce a tappable renewed 

 bark containing; the maximum amount 

 of rubber, in the shortest time. It may 

 be necessary to point out that it is the 

 function of a Botanical Department to 

 consider the permanence of the industry, 

 and not the immediate profit of indivi- 

 duals. 



T. Petch. 



ENTOMOLOGICAL NOTES. 



By E. Ernest Green. 

 Government Entomologist. 



The 'Black-headed Coconut Caterpillar' 

 (Nephanta seriyiopa, Meyr.) was again 

 reported from the Batticaloa district in 

 March. The pest may be considered to 

 be endemic in that locality. I doubt if 

 it is ever really absent, though it may 

 remain in abeyance for many months at 

 a time. The damage appears to be most 

 noticeable during the early part of the 

 year. With the exception of a single 

 (rather doubtful) case reported in 

 September, all other records have been 

 confined to the three months— March, 

 April and May. During a prolonged 

 study of the pest in 1906, 1 ascertained 

 that the eggs are usually laid amongst 

 the debris of the old galleries that shel- 

 tered the previous brood of caterpillars. 

 This fact emphasizes the importance of 

 stripping and burning the affected 

 fronds. I also satisfied myself that the 

 pregnant females were freely attracted 

 to light and could be captured in con- 

 siderable numbers by lamps set in trays 

 containing water with a sufficiency of 

 kerosene to form a film upon the sur- 

 face. I am convinced that the syste- 

 matic employment of these two methods 

 of treatment, during the critical period— 

 from the middle of February to the end 

 of May— will keep the pest in such check 

 as to prevent any widespread injury. 

 Bat, to be completely effective, the 

 treatment must be generally and 

 simultaneously adopted throughout the 

 affected area. 



With the greatly increased cultivation 

 of nitrogen-fixing plants, it is important 

 to note the species that are the most 

 free from insect attack. The experi- 



