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BRYCE : 
Near the centre wood vessels are absent, but they are 
produced in increasing number toward the outside. They are 
a little narrower in lumen than normal vessels, and are 
extremely tortuous. They have a longitudinal course in the 
nodule, and terminate abruptly at each end. They have 
large bordered pits as in normal wood. 
The libriform fibres are found at the ends of the nodule 
mainly, where the surface is very sharply curved. At these 
points wood parenchyma cells are at first produced, but the 
growth of the nodule entails a very rapid increase in surface. 
To meet this the cambium cells elongate, and cut off corre- 
spondingly elongated wood parenchyma cells. The elongation 
continues, and long prosenchymatous cells are produced. 
These cells are interwoven with one another, due perhaps to 
irregular elongation or curving of the cambium cells under the 
internal strains set up in the tissue by the growing nodule. 
Isolated cells can be obtained by maceration ; they exhibit 
many fantastic and bizarre shapes. These are the libriform 
fibres, but it is possible that in elongating some of the prosen- 
chymatous cells develop abnormal shapes, or that trac beides 
may also be thus changed. 
Over the rest of the surface of the nodule, with increasing 
girth, the wood parenchyma cells undergo a similar elongation, 
but to a lesser extent. A cambium cell undergoes for a time 
ordinary tangential division and consequent elongation ; it 
then divides radially, so that two daughter cambium cells are 
formed in its place. These undergo the same cycle in the 
further growth of the nodule. 
In large nodules the outer layers are nearly normal. 
Twisted and curved elements disappear, the vessels pursue a 
straighter course, and there is little to distinguish the sections 
from normal wood. 
The central core is sometimes excentric, owing to more 
rapid growth on one side of the nodule than on the other. 
The starch content of the wood parenchyma and medullary 
rays is often abundant. 
The vascular connections of nodules, which ultimately join 
up with the stem wood, are exactly similar to the vascular 
connections on globular shoots. The vestiges of such vascular 
