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BBYCE : 
cortex cuts easily. Correlated with the absence of stone cells 
in the outer cortex are the following : — The medullary rays 
are distinct, the latex vessels are continuous, and the difference 
between inner and outer cortex disappears to some extent. 
There is, however, a slight difference, in that the outer cortex 
has a greater abundance of tannin cells, and the cortical cells 
are isodiametric. Such differences in the structure of the 
cortex, more particularly the absence of stone cells in the 
outer cortex, could not be brought about by changes in the 
original cortex. Further, old nodules of large size effectively 
exclude the stem cambium for contributing cells towards the 
renewal of the cortex ; hence, in the course of time nodules 
would be exposed by the gradual shedding of the cortex as 
bark. Tissue thus shed as bark cannot be made good, unless 
the nodule cambium cuts off cortical cells. The fact that old 
nodules are not exposed, and the abnormal structure of the 
cortex covering them, indicate that the nodule cambium 
produces cortical tissue. This cortex produced by the nodule 
cambium may become very thick ; some specimens are almost 
twice the thickness of normal cortex. 
After a longer or shorter period of growth the nodule 
cambium develops a projection directed towards the stem 
cambium. The two cambia finally meet, merge into one 
another, and continue to produce wood cells internally. 
Thus, a bridge of wood cells is formed joining up the wood of 
the nodule with the wood of the stem. This may proceed 
simultaneously at several points on the same nodule and 
several connections be formed, but these remain isolated, 
hence the inner surface of the nodule never becomes wholly 
fused to the wood of the stem. In old nodules there are many 
connections, but there still remain areas of cortical tissue 
between the nodule and the stem wood. 
The writer has obtained radial sections of cortex in which the 
inward-growing projection of a nodule had a corresponding pro- 
jection proceeding outward from the stem cambium to meet it. 
Sections show that the inward-growing projection of a 
nodule may cause the stem cambium to lag behind in activity 
of division in its vicinity, so that a depression or pit is gradually 
formed in the stem wood. Generally the abnormal strains 
