August, 1910.] 



123 



Plant Sanitation- 



ary courses of botany. A short length 

 of a willow branch is completely ringed 

 near the base and is suspended in a giass 

 vessel in moist air. The ejcperiment is 

 designed to prove that the food stored 

 in tue upper part of the twig caunot 

 pass into the part below the ring ; but 

 incidentally it shows that in the damp 

 atmosphere an enormous development 

 of " callus," i.e., of wound-healing tissue 

 occurs, much more than would be the 

 case in a dry atmosphere. Therefore, as 

 far as the simple healing of a wound 

 is concerned, it may be expected to take 

 place more rapidly when the air is moist 

 than when it is dry. There is just one 

 possible flaw in the argument ; the pro- 

 cess of bark renewal, when the tapping 

 has been done carefully and the cam- 

 bium is uninjured, is not exactly the 

 same as the processes involved in healing 

 over wounds which extend to the wood. 



The second factor to be considered is 

 the amount of food in the tree which is 

 advisable for the formation of the re- 

 newed bark. This food is practically all 

 stored in the tree before tapping begins, 

 and the tree draws on this reserve to 

 provide material for the formation of 

 new bark. Professor Fitting's investi- 

 gations would seem to show that nothing 

 is added to the store during tapping ; 

 the tree consumes the food it is then 

 manufacturing and draws on its reserve 

 as well. Now, the amount of reserve 

 food in a young Hevea is astonishingly 

 large, and whether the trees are widely 

 or closely planted it is quite sufficient 

 to ensure bark renewal. Therefore for 

 the first renewal the two trees will be 

 practically equal as far as their food 

 reserve is concerned, while the closer 

 planted have the advantage of a damper 

 atmosphere. The latter may, therefore, 

 be expected to renew their bark more 

 rapidly. In subsequent renewals, how- 

 ever, the advantage is with the widely 

 planted trees. When the closely plant- 

 ed trees grow up, their crowns interfere, 

 and ultimately become mere bunches of 

 leaves at the top of a long stem. A 

 crown of this kind cannot form an ade- 

 quate supply of reserve food, and there- 

 fore the bark renewal must be slower. 

 The influence of a damper atmosphere 

 cannot compensate for lack of food. 



Hevea interplanted with cacao is, as 

 far as the tapping area is concerned, in 

 a damper atmosphere than if the Hevea 

 had been planted throughout instead of 

 cacao. Moreover, siuce it overtops the 

 cacao, the factor of diminished food 

 supply through interference of the 

 crowns of adjacent trees does not enter 

 into consideration. It is to be expected, 

 therefore, that bark renewal on such 



rees will be more rapid than on widely 



planted Hevea. But the advantage is 

 one that cannot be made use of, since 

 the disease factor puts mixed Hevea 

 and cacao planting quite out of the 

 question. 



The subject of bark renewal has been 

 discussed above, quite apart from any 

 consideration of diseases, If diseases 

 are taken into account, the damper 

 atmosphere of a closely planted area 

 must be regarded as a decided disad- 

 vantage, as it has already been proved 

 in the case of cacao. But the details 

 given are sufficient to show that it is 

 not advisable to lop Hevea with the 

 express intention of allowing the sun to 

 have access to the stems and so favour 

 bark renewal, Ther e might be cases of 

 disease in which it would be necessary, 

 but as a general practice it would defeat 

 the object desired. 



The system of tapping one quarter of 

 a tree at a time by what is practically a 

 half-herring bone is now largely followed 

 in Ceylon. On some of our best estates 

 the system is varied by tapping for three 

 months on one side of the tree, then 

 three months on the other side, etc. In 

 a recent publication, Gallagher states 

 that similar changing applied to the full 

 herring bone is wasteful since each cut 

 must be tapped at least three times 

 before a normal flow of latex begins. 

 There is, however-, a difference between 

 the Ceylon system and that condemned 

 by Gallagher. In the latter, one-half of 

 the herring bone is tapped for three 

 mouths, and then two months' rest is 

 given before the other half (of the same 

 herring bone) is tapped. It would 

 appear, therefore, that the delay in 

 obtaining a normal flow is due to the 

 two months' rest. 



It would, however, be interesting to 

 know whether any similar result is 

 experienced in Ceylon when the tapping 

 is changed from one side to the other. 

 As the change is made at a definite time 

 any diminution in yield would certainly 

 be noticeable. Theoretically it would 

 appear that there should not be any 

 diminution. When Parkin experi- 

 mented on the Henaratgoda trees, he 

 tapped by separate V's, making them 

 each time four to six inches from the 

 former V's. Y"et he obtained a regu- 

 larly increasing flow of latex, just as is 

 obtained by re-opening the same cut. It 

 would seem from this that, provided 

 the tapping is continuous (Parkin tapped 

 every week), a normal flow should be 

 obtained on whichever side the tree is 

 tapped. 



Now that the history of rubber culti- 

 vation is under discussion, it may be as 



