18 
PEOFESSOE W. C. WILLIAMSON ON THE OEOANIZATION 
than real, since in the former the radial inward prolongations of the bark ( h ) never 
become occupied by vascular structures, whilst, I need scarcely add, the morphology of 
the cortical layers in the two cases is altogether different. 
Branches. — In the present state of our knowledge I am unable to ascertain whether 
figs. 24 & 25 are branches of stems like fig. 23, or correspond to its terminal portions ; but 
be that as it may, I have obtained independent proof that at least one class of branches is 
given off from similar stems, besides which we have many indications of the existence of 
another and apparently very different set of secondary lateral vascular bundles. Figures 
32, 33, & 34 represent three very instructive transverse sections of one stem, in which 
the various stages in the development of the branch can be easily traced. These sections 
were made at intervals of little more than the sixteenth of an inch apart. Fig. 32 is 
the lowest of the series. The vessels of the central axes have been partly destroyed, and 
the epidermal layer and some of the subjacent outer cortical layer are also wanting. In 
other respects the section exhibits in a beautiful manner the more characteristic features 
of this plant. The two primary vascular wedges ( c , c') also present much of their usual 
appearances ; but we find that the inward prolongation of the cellular bark ( h ') sepa- 
rating these two wedges, instead of attaining to its usual dimensions, is narrowed to two 
or three radial rows of cells (h), being encroached upon by a mass of obliquely inclined 
vessels (x), which exhibit every appearance of being given off from the left-hand side 
of the primary vascular wedge ( c ), and of ascending obliquely from right to left. In the 
next higher section (fig. 33) the two vascular wedges ( d , d') have been pushed widely 
asunder, and the triangular area between them is now occupied by a number of mean- 
dering vessels intermingled with a little cellular tissue. These vessels are proceeding 
outwards to a semicircular mass of vessels, of which those occupying the centre, whence 
the others radiate, are arranged without order, like those of the central axis ( c ) of 
figs. 23 & 26 ; and the rest are distributed in radiating series, forming numerous exoge- 
nous laminae and wedges separated by many medullary rays (f). On turning to the third 
section in the ascending series (fig. 34), we find that the two wedges ( c ' , c ") have resumed 
their normal positions, and that the wedge of cellular bark intervening between them 
exhibits little or no difference from the corresponding tissue separating the other vascular 
wedges of the section, save that one or two detached radiating laminae of small vessels 
pass outwards through its parenchyma. The lateral vascular laminae of the two woody 
wedges, which are in immediate contact with the intervening bark, have not quite 
recovered the regularity of radiating arrangement which characterizes them elsewhere. 
This disturbance of the order is especially seen near the peripheral margin of each wedge. 
The branch itself now consists of a normal central axis, with its exogenous wedges arranged 
around that centre, so as to form a complete circular cylinder, which is now entirely 
separated from the vascular portion of its parent stem by the intervention of a mass of 
the coarse outer cortical parenchyma (i). The radiating series of vessels constituting 
the exogenous portion of the branch are still seen to be separated by numerous medul- 
lary rays of nearly equal size, the separation of these vessels into the six groups seen in 
