400 
PROFESSOR AN. C. WILLIAMSON ON THE ORGANIZATION 
medullary vasculo-cellular axis, g the pseudocambium or innermost bark, h the parenchy- 
matous bark, and the dark shaded outline, k, the peripheral prosenchyma. Six vascular 
bundles are indicated by corresponding numerals, the same numeral being attached to 
the same bundle in each section. We thus see that in Plate XXX. tig. 37 there is one 
bundle (3) enclosed within the innermost bark ; 1, 4, and 6 are external to, but in almost 
immediate contact with, its outer surface ; whilst 2 and 5 are in the parenchymatous layer 
at a little distance from the pseudocambium. Bundle 1 retains its unchanged position 
in all the sections up to fig. 42 ; in each of the remaining two the section is imperfect, and 
this bundle has been lost. Bundle 2, on the other hand, is seen in all the sections ; but 
it also occupies nearly the same position in fig. 44 that it does in fig. 37, as well as in 
the intermediate ones. Bundle 3 first appears in fig. 37 enclosed within the pseudocam- 
bium layer, but entirely separated from the vasculo-cellular medullary axis : in fig. 38 
it is imbedded in the substance of the inner bark ; in fig. 39 it has escaped through 
that innermost bark-layer, and now rests upon the outer surface of it ; which position 
it retains undisturbed up to the uppermost section, fig. 44. Bundle 4 occupies 
the same unaltered position throughout the entire series. The same remark applies 
to bundle 6 in the first six sections, in which it is present, it having disappeared 
from figs. 43 & 44, from the same cause as that which has removed bundle 1. Bundle 5, 
on the other hand, not only appears in all the series, but has undergone important 
alterations of position in the interval separating figs. 37 & 44. Following these 
sections in their numerical order, we see that this latter bundle has moved steadily 
outwards, until in fig. 43 it only appears as a semidisorganized mass external to the 
prosenchymatous layer of the bark. 
We further learn that the changes in the position of the latter bundle have been 
accompanied by some correlate changes in the bark itself. In Plate XXX. fig. 37 the 
prosenchymatous layer of the bark external to bundle 5 is rather thinner than usual, 
forming a conical protuberance which projects slightly beyond the general peripheral 
outline of the stem ; at the base of the conical portion a prolongation of the prosenchyma 
extends obliquely inwards to the right, whilst the same layer is also somewhat thickened 
on the left hand of the apex of the cone. As we proceed towards fig. 40 we find that 
the prosenchyma to the left hand of the bundle gradually thickens, until it forms a 
prominence which projects inwards, precisely like that already noticed as existing to the 
right of the bundle in fig. 37. In fig. 41 we discover that the bundle is fairly within a 
circumscribed area, which resembles in form a section of the base of a Lepidodendroid leaf. 
In fig. 42 the bundle has reached the centre of this area, besides which the outermost 
bark (k) immediately external to the bundle is now becoming disintegrated. In fig. 43 
the process has gone still further. The half-decomposed bundle can now scarcely be 
identified, encompassed as it is, in the original section, by the foreign vegetable debris 
which surrounded the entire stem. The thin bark-layer (k) seen in fig. 42, has wholly 
disappeared, and the two projections of the outer bark (Id Id) are rapidly converging to 
produce that complete closure of the interruption to its continuity which is seen in fig. 44. 
