276 
BRYCE : 
vessels over a large area. Nodules occur, which branch and 
have a distinct net structure ; there are open meshes where 
growth has proceeded along the latex vessels only, and left 
the intervening cortical tissue unchanged. This intervening 
cortical tissue consists of medullary rays, as the meshes 
formed by the ramifications of the latex vessels in normal 
cortex are occupied by the medullary rays. 
In gouging a nodule out of the cortex a brown point is 
frequently observed at each end of the nodule, and this is 
seen to coincide with a similar brown point in the cortex. 
These brown points are the altered latex vessels and their 
neighbouring cells. The central core of the nodule is here 
continuous with the cortical tissue ; the nodule would pro- 
bably continue its growth along the latex vessels thus altered. 
In nodular cortex, which is still more or less normal, longi- 
tudinal sections show the presence of vertical areas of abnormal 
tissue consisting entirely of parenchymatous cells. These 
areas differ from the surrounding tissue in being free from 
tannimand stone cells, and in having abnormally curved cell 
walls. They appear to arise as the result of indefinite cell 
division over a small area, and occur generally between the 
inner and outer cortex. The medullary rays are quite 
distinct in the cortical tissue on either side of the abnormal 
area, and can sometimes be traced through it. This indicates 
that these areas arise subsequently in the cortex. They stand 
out prominently in sections as white areas amid the sur- 
rounding tannin-stained tissue. It might be suggested that 
the cortex is stimulated to this indefinite cell division by the 
presence of irritant substances diffused from the altered latex 
vessels, or that bud primordia are stimulated to growth and 
develop abnormally. Such abnormal areas have no definite 
cambium, and twisted cells with curved cell walls occur, which 
resemble the twisted tracheides of nodules, but are not 
lignified. Occasionally these areas are produced in the inner 
cortex near the stem cambium, when the cells of the inner 
cortex may be displaced and disposed in undulating lines, 
giving a tissue which strongly resembles that in the vicinity 
of developing vascular connections. In one case sections 
showed a developing bud structure with a definite cambium 
