The diseases and pests of the rubber tree . n may increase in size until they become large, more orless hemispherical, or cyhndrical masses. If several of thesesmall nodules occur close together their cambium layersmay meet and unite, thus producing a multiple nodule, butsuch a one would generally even up in further growth intothe same shape as the foregoing. Often a large nodule inthe course of its growth meets and fuses with small nodules,and the latter then appear as excrescences on the surface ofthe larger. Instances of the fusion of small nodules are shown VI NON-PARASITIC
The diseases and pests of the rubber tree . n may increase in size until they become large, more orless hemispherical, or cyhndrical masses. If several of thesesmall nodules occur close together their cambium layersmay meet and unite, thus producing a multiple nodule, butsuch a one would generally even up in further growth intothe same shape as the foregoing. Often a large nodule inthe course of its growth meets and fuses with small nodules,and the latter then appear as excrescences on the surface ofthe larger. Instances of the fusion of small nodules are shown VI NON-PARASITIC DISEASES 183 on Fig. 23. In this way a sheet of wood may be formed,though it would appear that, as a rule, the sheet nodulesbelong to the second type. In the second type the nodule at first is a network ofwood, or a sheet perforated with small holes, whichever onechooses to regard it. Such a sheet may be only a millimetrethick, yet it may extend up the stem for a length of severalfeet. At first it is embedded in cortical tissue, the latter. Fig. 23.—^Nodules; earlj stages. Natural size. being continuous from side to side of the nodule through theperforations, but as its cambium adds new layers of woodthe holes are closed up, and it becomes a thin continuoussheet, sometimes with depressed lines here and there whichmark the sites of previous holes. The most remarkablefeature about these plates is the large area they extend overwhile they are still so thin that they can scarcely be extractedentire. When these plate nodules thicken, the resulting burrmay be several feet in length, but comparatively sUghtlyelevated. One such nodule, taken from a tree which had 184 THE RUBBER TREE been tapped by a prickmg method, was 4 feet 9 inches long,6 inches broad, but only 1 inch thick. The surface of a nodule is usually marked with raised ridges, running in par-allel undulating lines, andhere and there formingclosed curves. A similarpattern sometimes occurson the stem wood behindthe nodule.
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