RUBBER (HEVEA) DISEASES 71 
inches in size. If several spherical nodules develop near each other 
their cambium becomes united, the wood of each fuses with that of 
its neighbor, and a multiple nodule results. Secondary nodules 
may later appear on the larger ones, so that the entire mass be- 
comes very irregular. 
The flat perforated plates are of rare occurrence. However, they 
are difficult of detection in early stages and may be overlooked. 
They are most remarkable when separated from the cortex and ap- 
pear in some cases as little more than a network of woody strands. 
As neAV layers of wood are formed the openings are closed, and the 
structure assumes the nature of a thin plate. This plate is never 
plane but is marked by indentations, grooves, and circular striatums. 
These plates while unattached in the cortex are seldom more than 
a millimeter thick, with a breadth of 2 or 3 inches. They may ex- 
tend vertically from a few millimeters to several centimeters. The 
cambium of these plates eventually fuses with that of the main stem. 
Conical points of wood develop on the inner surface of the plates 
which eventually fuse with the wood of the main stem. In some 
cases this fusion continues until the plate is more or less uniformly 
attached to the main trunk. Ordinarily, however, the plate remains 
embedded in the cortex or is attached at only a few points. The 
plates are very rarely developed singly. On badly tapped trees they 
may occur in groups or be developed parallel to each other, causing 
the tree to appear secondarily fluted between the callous ridges. The 
location of these plates may be detected either by the presence of 
elongated swellings or by a slight roughness of the bark in ad- 
vanced stages. In a few cases where the fusion with the main trunk 
did not take place, a layer of dry rubber may form between the two, 
owing to the fact that the latex in the cortex between the stem and 
the plate is forced out as the plate develops, and the latex coagulates 
in situ. The cortex covering such plates is usually rough with 
longitudinal fissures and contains little or no latex. 
Bateson has pointed out that these nodules were formed around 
old latex vessels whose contents had undergone some kind of chemical 
change. This alteration of content causes the formation of cambial 
cells around the affected vessels, and they are soon enveloped by a 
layer of wood. If a small nodule is sectioned, a small brown speck 
is discernible in its center, or the discolored tissues may appear as a 
line half way between the surfaces of the flat plates. If the dis- 
colored tissues are microscopically examined, it will be seen that they 
consist of cortical parenchyma, or more rarely sclerenclryma cells. 
The surrounding wood elements are more or less regular in shape, but 
they become less so the nearer the cambium is approached. The 
concentric structure of the nodules is conspicuous in cross section. 
Depending upon the number or extent of the affected latex vessels 
the nodules are spherical or flattened. If the vessels are affected over 
a large area, the nodule will take the form of the perforated plates, 
which is merely the modification of the latex system of one year's 
development. If the character of alteration in the latex system 
causes a coagulation of the latex in the intercellular spaces, the fact 
may be detected by finding cortical cells embedded in a ball of dry 
rubber in the center. Lesions of various kinds in the cortex into 
which the latex has flowed and has there coagulated, initiating the 
formation of nodules, are of common occurrence. 
