480 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
with inorganic matrix, and the transverse diaphragm or septum of cellular tissue marking 
the node (Plate XXIV. fig. 10, i) *. It has been supposed by more than one writer 
that the fistular cavities did not exist in the living plant, but that they were the result 
of disorganization and decay. Such, however, is certainly not the case. The sharply 
defined outlines and exquisite preservation of their innermost cells demonstrate that no 
such decay has affected these specimens. In its very young state the pith was solid and 
unbroken — a fact demonstrated by the specimen represented in Table 3, fig. 7 of Mr. 
Binney’s Monograph already referred to. But the small size and exceeding rarity of all 
such specimens demonstrates that the rapid growth of the woody axis caused the pith to 
become ruptured and fistular at a very early period. The process thus commenced ended 
finally in a complete absorption of the pith, explaining some points in the history of 
these plants of which no explanation has hitherto been found. On looking vertically 
at the cellular diaphragm (fig. 10, n), we discover that whilst its more peripheral portions 
consist of elongated cells like those common to the rest of the pith, in its thinner 
central part we have a very regular and delicate form of parenchyma (fig. 7). Some 
writers consider that they have found vascular tissues in the pith. I have not done so. 
The Woody Zone. — This, as we have seen, is a zone of variable thickness, consisting of 
a series of wedges composed of vascular and cellular tissue combined (fig. 1 ,f), separated 
from each other by cellular prolongations of the pith (fig. 1, c ), in which the cells have 
a special permanent arrangement. Every woody wedge commences, at its apex, which 
is directed inwards towards the centre of the stem, at a narrow canal (fig. 1, e) of uniform 
diameter, and which runs in a direct vertical line from node to node. These several 
parts requires a separate examination. Each wedge extends vertically in a straight line 
(fig. 2 ,f), the length of the internode. It consists of a series of laminse which increase 
in number as we proceed from within outwards from the intercalation of additional ones ; 
hence the widening of the broad external base of the elongated wedge. Each separate 
lamina is composed of a linear series of vessels, disposed in a radiating line (Plate XXIII. 
fig. 9,/). In the transverse section, these vessels appear to be nearly square (fig. 6, g), 
whilst in the longitudinal one they exist as elongated, unbranched tubes (fig. 5,g), which 
are sometimes reticulated (fig. 4), and at others transversely barred. Very varied names 
have been assigned to these tubes by different authors. Mr. Binney speaks of them as 
“ pseudo-vascular ,” and Dr. Dawsox and Mr. Carruthers as “ scalariform ” tissue, neither 
of which terms appears to be exactly appropriate. They are unquestionably modified 
forms of spiral tissue, though we have every reason to believe that they were incapable of 
being unrolled ; but they are not scalariform, in the sense in which the term is applied 
to the vessels of ferns and some other living Cryptogams, since they do not exhibit angles 
thickened by continuous ligneous deposits as is seen in those examples. Still less should 
they be designated pseudo-vascular, since they are true vessels. The term “ barred ” 
* YVe have in this specimen a curious illustration of the fact that this pith was fistular whilst the plant stood 
erect, inasmuch as a number of vegetable spores (fig. 10, x) have found their way into the cavity, and now rest 
upon the diaphragm which has arrested their further descent. 
