FOEMATION OF NODULES. 
269 
{a) Central Core. 
The central core, in transverse sections, appears to the imked 
eye as a dark brown point or line, and in longitudinal sections 
as a brown line or plate respectively. It consists of one or 
several latex vessels surrounded by cortical cells containing 
a dark brown tannin, and outside these a few cortical cells 
without tannin. 
In normal cortex transverse sections show the latex vessels 
disposed in concentric rings ; thus, in a length of stem they 
could be represented diagrammatically by a series of cylinders 
fitting one inside another, but separated from one another by 
approximately equal spaces. While the latex vessels of any 
one cylinder branch and anastomose abundantly within that 
cylinder, they do not form any connections with latex vessels 
of neighbouring cylinders. Each cylinder is thus completely 
isolated from adjacent cylinders. The latex vessels are 
accompanied by prosenchy matous cells, some of which have 
a tannin content ; such tannin cells are isolated or occur in 
little rows. The latex vessels with their prosenchymatous 
cells and the sieve tubes and companion cells pursue a parallel 
course ; when they encounter a medullary ray in their vertical* 
course in the cortex, they diverge and pass round it. In 
tangential sections, therefore, the medullary rays appear to 
lie in pockets or enclosed areas formed by the latex vessels, 
prosenchymatous cells, sieve tubes, and companion cells. 
In a nodule the central core shows all these points of 
structure. The latex vessels in the core are derived from 
only one latex cylinder, as there is only a single row of them. 
They are accompanied by prosenchymatous cells, and in 
longitudinal sections the medullary rays are observed to 
lie in pockets formed by the latex vessels, prosenchymatous 
cells, sieve tubes, and companion cells. The tannin cells here 
completely surround the latex vessels in varying numbers, 
but much more abundantly than in normal cortex. The 
central core thus consists of a patch of cortical tissue, which 
has been encysted by the formation round it of a cambium 
which produces wood cells. 
The presence of latex vessels can be demonstrated by 
staining and maceration. The rubber content stains pink 
