290 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
piles of uniform width is not a result of the same polarizing tendencies in the primitive 
tissues as those which led the cells of the latter to arrange themselves in a similar 
manner to form the barred vessels. In the latter the conversion into vessels has been 
completed. In the former the cells remained unconverted; hut they have not only 
retained the primary disposition to assume the columnar form, but the same tendency 
reappears in all the new cells subsequently formed in the enlarging pith. 
Whilst the large specimens last described are almost invariably accompanied by some 
portion of their bark, which surrounds them as a flattened cylinder, I have in no one 
such instance obtained so perfect examples of this bark as in the specimen represented 
by Plate XLI. fig. 1 ; the tissue is usually limited to its outermost part, viz. to the sub- 
epidennal parenchyma and a small portion of the subjacent prosenchyma. The example 
Plate XLII. fig. 11 was so surrounded, a small portion of the bark being seen at i. 
Fig. 15 a represents a vertical section of a fragment of bark from the same specimen; 
to the left of the figure we have the two tissues (i and Jc) just referred to, whilst at l 
are the persistent bases of the petioles, which remain in situ in this plant, as in Coeda’s 
genus Lomatophloios. In this figure, which represents the object of its natural size, 
the leaf-petioles are small, though larger than in the bark of fig. 9 ; but I have specimens 
in which they are fully three times the size shown in fig. 11. Thus it will be seen 
that I have these leaves in every gradation of size, from the imperfectly formed one of 
Plate XLI. fig. 2, to large ones which, though their extremities have been broken off, 
have their basal petioles five eighths of an inch in length. But though large stems 
rarely have the bark in situ and in perfect condition, Mr. Geieve has sent me several 
large masses of it, so that it does not appear to be a scarce object. But it usually 
occurs in a remarkable state, being deeply fissured longitudinally, and partially broken 
up into long wedge-shaped masses, linked together at their broad bases — a probable 
result of desiccation. 
In the transverse section, that which appears to be identical with the inner parenchy- 
matous bark ( h ) of the young twigs merely appears as an ordinary form of parenchyma; 
its usual aspect in radial sections is shown in Plate XLIII. fig. 16; it consists of innu- 
merable square cells, slightly elongated vertically, and exhibiting some disposition towards 
an arrangement in perpendicular lines, reminding us of what is seen in Plate XLI. 
figs. 6 & 7, It. The prosenchymatous layer is easily identified with the layer i in the two 
figures just referred to. It is very thick, and the cells vary in form, being sometimes 
much larger, as well as more fusiform, than at others ; whilst towards the exterior of the 
layer radial sections exhibit in a very marked manner the arrangement of prismatic cells 
seen in Plate XLIII. fig. 17. These cells are elongated vertically in a very regular 
manner, having a uniform diameter from end to end of about '0025. Their length varies 
greatly : sometimes, though not often, they are almost square ; at others they are so much 
elongated, especially at the outer portion of the layer, that they almost assume the form 
of vessels; but what gives them their remarkable appearance is the fact that clusters of 
them have exactly the same length, and are arranged in the same radial plane, causing 
