Les maladies et ravageurs de l'arbre à caoutchouc . Fig. 33.-^une plaie, la foudre x J. couches externes de l'écorce sur les hautes branches, apparentlysomewhat de manière identique à celle connue sous le nom de chancre haut inCeylon. La Rutgers considère que c'est probablement dû toKghtning. Où la foudre a simplement woimded un arbre la cause la plaie est révélé par thehealing sont caractère particulier de processus. La marge de la plaie, de l'mosttopical espèce, montre une double cal. L'effet de l'thelightning n'est pas seulement de séparer l'écorce et le bois forums radialement courte distance, mais aussi de diviser en interne sur une smallarea le long e

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The diseases and pests of the rubber tree . Fig. 33.—^A lightning wound, x J. outer layers of the bark on the upper branches, apparentlysomewhat similarly to that known as top canker inCeylon. Rutgers considers that this is probably due toKghtning. Where lightning has merely woimded a tree the causeof the wound is revealed by lie peculiar character of thehealing process. The margin of the wound, in the mosttopical case, shows a double callus. The effect of thelightning is not only to split the bark and wood radially fora short distance, but also to split it internally over a smallarea along the line of an annual ring. New growth of tissuethen occurs from the cambium at the edge of the wound, as NON-PARASITIC DISEASES 203 in tlie case of ordinary wounds, and also from the separatedsurfaces of the wood along the line of the annual ruag.. Fig. 34.—^Cross-seotion of a lightning wound (diagrammatic). Figure 33 shows a short oblique wound, caused bylightmng, in process of healing, and the accompanyingdiagram (Fig. 34) was drawn fromthe cross-section of it. The woodis indicated in the diagram byradial lines, and the cortex bythe dotted areas. The project-ing edges of the original cortexhave died back, and a growth ofcallus has taken place over theedges of the wound from theoriginal cambium. In addition, there is new growth (indicatedby dose lines) on either side ofthe wound in the split along thelast annual ring. The blackregions in the latter situationindicate dead tissue. The illustrations describeddepict a well-defined case. Butmany instances occur in whichthe sear is small, and no openwound is evident. In these casesthe outer bark is often notcracked, and nothing is observeduntil it scales off and reveals thehealed scar. Such occurrencesare fairly common in one dis-trict in Ceylon, especially ontwo estates on opposite

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