The diseases and pests of the rubber tree . ctions from the pointof origin. Crops of smallnodules frequently occurround large nodules,especially when they aregrouped in have not, how-ever, been observed on the parts of the tree below ground, norhad they been found on exposed lateral roots, even in caseswhere the stem was badly burred down to the ground level,before the appearance of the nodules following Brown cutting across a small nodule, a dark-brown point orline is found in the centre. In the case of thin plate nodulesa line extends along the middle of the nodule,
The diseases and pests of the rubber tree . ctions from the pointof origin. Crops of smallnodules frequently occurround large nodules,especially when they aregrouped in have not, how-ever, been observed on the parts of the tree below ground, norhad they been found on exposed lateral roots, even in caseswhere the stem was badly burred down to the ground level,before the appearance of the nodules following Brown cutting across a small nodule, a dark-brown point orline is found in the centre. In the case of thin plate nodulesa line extends along the middle of the nodule, almost fromside to side, but in small, spherical pea nodules only aminute brown point may be evident. This coloured point,or line, is the section of a line, or sheet, of cortical tissueround which the nodule has been built. As was first shownby Bateson, and confirmed by Bryce, this browned tissueconsists of one or more latex vessels, surrounded by cellswhich contain a dark-brown tannin, and outside these a fewcortical cells without Fig. 24.—Nodules, x J. VI NON-PARASITIC DISEASES 185 The formation of nodules, in the most general case, isdue to an alteration in the contents of the latex walls of the latex tubes become yellow, and the neigh-bouring cortical cells are filled with a brown tannin. Thissets up an irritation in the surrounding tissues, with theresult that a cambium is formed, which buries the abnormallatex vessels in a mass of wood. If only a short length ofthe latex vessels is concerned, the nodule is at first small andspherical or cylindric, but when the latex vessels are alteredover a large area a plate is formed, or the vessels are encrustedin such a way that the nodule assumes the network patternof the latex vessel cylinder. The altered latex vessels whichare enclosed in the nodule belong to one latex vessel cylinder,or row, only. The cause of the alteration in the latex vessels has notbeen discovered. It has not been found to be associated
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