The diseases and pests of the rubber tree . Similarinstances have occurred in Tea. Rutgers has investigated the effect of lightning on Heveain Sumatra, where injury due to this cause is by no meansrare in some districts. He classifies the effects under fourheads: (1) Siagle trees, or groups of trees, may be killed. Insome instances one tree is killed, while the branches of thetrees nearest to it are withered. In other cases one ormore trees are killed, and the tops of the neighbouring treeswither, as in Die-back. The bark may be killed in a longi- 202 THE RUBBER TREE tudinal strip, sometimes n
The diseases and pests of the rubber tree . Similarinstances have occurred in Tea. Rutgers has investigated the effect of lightning on Heveain Sumatra, where injury due to this cause is by no meansrare in some districts. He classifies the effects under fourheads: (1) Siagle trees, or groups of trees, may be killed. Insome instances one tree is killed, while the branches of thetrees nearest to it are withered. In other cases one ormore trees are killed, and the tops of the neighbouring treeswither, as in Die-back. The bark may be killed in a longi- 202 THE RUBBER TREE tudinal strip, sometimes nmning spirally down the stem,and the dead strip is soon attacked by borers. (2) Trees which, have been struck by Lightning, but notHUed, may bear short vertical wounds on the stem, some-times arranged in a spiral Une. These may be accompaniedby a wound at the collar. (3) The exudation of latex from the upper branches isregarded by Rutgers as another form of injury caused bylightning. (4) The fourth type of injury is the scaling ofE of the. 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.
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