696 
PROFESS OB W. C. WILLIAMSON ON THE ORGANIZATION 
The vertical section represented in Plate LVII. fig. 43 exhibits a vascular bundle (to) 
going off to some lateral appendage ; and it will be observed that it has carried along 
with it a narrow investing cylinder of the innermost bark (g) enclosed in a broader one 
of the middle parenchyma ( A ). I have already referred to the arrangements of the 
outermost vessels (a", a") of the two lateral arcs of Plate LYI. fig. 42, as well as to the 
supposition of M. Renault that these tissues might possibly become detached from the 
main bundle to supply lateral ramifications of the frond. My specimens demonstrate 
the correctness of this inference. Fig. 43, to, shows that such bundles are given off, and 
that after leaving the central vascular axis they diverge rapidly outwards. On the 
right hand of fig. 42, as already observed, we see these vessels ( a ") but little removed 
from their corresponding lateral arc, whilst to the left the similar vessels (a') are wholly 
detached from their arc (a), and almost reach the inner surface of the cylinder of 
middle bark ( A ). In Plate LVII. fig. 45 we have a transverse section of another of 
these vascular axes. At the one extremity we have a large continuous band of small 
vessels (a") occupying nearly their normal position, but at the opposite end we have 
only two small detached clusters of such vessels (a 1 , a'), their central connecting group 
having disappeared : Plate LVII. figs. 46 & 47 and Plate LVIII. fig. 48 explain these 
conditions. These figures represent portions of three transverse sections of the same 
petiole made at points about the eighth of an inch apart. Fig. 46 is a segment of the 
bark of the lowest of the series, and in it we see that the two vascular masses (to", to") 
have just entered the middle bark (A). At this point they are located in one common 
oblong areola ( g ), which was formerly occupied by an extension of the innermost cortical 
cells. Each of these vascular bundles still exhibits the irregular outline and somewhat 
square form that we see at a 1 on the left-hand side of Plate LVI. fig. 42. The middle 
and outer cortical layers are here unaltered. Plate LVII. fig. 47 exhibits one extre- 
mity of the central vascular bundle (a), which presents the appearances already referred 
to in the instance of fig. 45, a i ; viz. there are two detached clusters of small vessels left 
(a! & a 1 ) ; but those central vessels which ought to link these two detached clusters 
into one linear group (as at fig. 45, a") have gone to form the two bundles already seen 
at fig. 46, to", to". In fig. 47 we find that these bundles (to", to") have not only pene- 
trated further into the bark, but the section of each of them has now assumed a cylin- 
drical form, whilst the single areola within which they were enclosed in fig. 46 is now 
divided into two, separated by a band of the parenchyma of the middle bark (A). The 
bark has also become enlarged at this point. In Plate LVIII. fig. 48 this enlarge- 
ment of the petiole has increased yet more. We now find the ordinary parenchyma of 
the middle bark at A. At A' we have a layer of small cells like those seen near the peri- 
phery of the petiole ; at A' we have a second mass of middle-bark parenchyma, and at k 
we have the ordinary prosenchymatous cells forming the outermost layer of the stem. 
The layer of small cells at k' seems to indicate the approach of the entire separation of 
the lateral branch or branches from the primary petiole, and the reappearance in the latter 
of the two layers of middle and outer barks, A & k' , in their normal positions and dimen- 
