FOÊMATIOÎÎ OF NODULES. 
275 
set up in the cortex by the growth of the nodule would result 
in irregular cambial activity, and thus ultimately in a pitted 
and warty surface. This is probably the mode of origin of 
the majority of the pittings on the stem wood and on the 
nodule. 
Nodular Cortex. 
Under this heading will be considered cortex in which 
nodules are developing. Sections of nodular cortex showing 
early stages of nodule formation can be readily obtained. 
Round a developing nodule the cortical tissue is much com- 
pressed and distorted. Cells are pushed outwards from the 
centre of formation and come to lie concentrically round the 
nodule. Sometimes stone-cell groups are thus displaced and 
form an almost complete ring, or an entirely complete ring, 
round the young developing nodule. It is obvious that the 
formation of a nodule sets up in the surrounding cortical 
tissue unusual internal strains, which would have an imme- 
diate effect on dividing cells and even on mature cells. This 
probably accounts for the abnormal shape of cells sÉid the 
abnormal curvature of cell walls often seen. The inner 
cortex is in nearly every case quite normal ; nodules originate 
in the outer cortex at varying distances from the inner cortex, 
or very rarely in the inner cortex. 
Old nodules are often of considerable size and of various 
forms ; roughly, they form either plates or rounded masses of 
nodule tissue. Sections through the central core show that 
cell division begins simultaneously round several adjacent 
latex vessels in the same cylinder, and that the several cambia 
on coming into contact merge into one another and form one 
continuous cambium round the whole. A large nodule in its 
development may come in contact with small nodules near it 
and fuse with them. This is plainly seen in the external 
appearance of some nodules which seem to have small nodules 
adhering to them ; sections show that the central core of the 
small nodule is not connected with that of the large nodule. 
By such continued fusion, plate or sheet nodules may arise ; 
but more often these appear to arise by the growth of a nodule 
from its point of origin along the ramifications of a latex 
vessel cylinder or by simultaneous encrusting of the latex 
