OF THE FOSSIL PLANTS OF THE COAL-MEASUEES. 
689 
its place occupied by a number of the small barred vessels which so nearly surround 
it. In Plate LIV. fig. 30, a\ the crescentic vessel is rather different in form from what it 
generally appears to be. It is brought into close contact with the very slightly convex 
adjoining face of the hour-glass bundle, its own inner surface for nearly the central 
half of its length being also flattened, whilst its two extremities are incurved. These 
arrangements appear to me to be too symmetrical to be merely the accidental results of 
pressure. In Plate LV. fig. 35 this crescentic bundle is broken up into two (a', a!) ; and 
that this subdivision also is not the result of violence, but is a normal organic state, is. 
shown by the circumstance that each half has its ends curled inwards in the same 
crescentic manner as characterized the two ends of the bundle a' of fig. 30 — a fact 
which, as we shall see immediately, has a physiological significance. 
The cortical investment of these bundles closely resembles that of the Rachiopteris 
Oldhamia. We have in both a delicate inner parenchyma (fig. 28, g), usually more or 
less destroyed, a thick middle portion consisting of a coarse parenchyma (h), and an 
outer dense prosenchymatous layer (1c). In the plant under consideration very little of 
the innermost tissue ( g ) remains. In one example it is preserved in the canal-like 
groove (a"), and in several I find small portions of it in contact with the bundle. All 
these indications tell the same tale, viz. that it exhibits the common aspect of paren- 
chyma, but with smaller and somewhat more delicate cells than those which constitute 
the middle portion of the cortex. This latter structure (h) is exquisitely preserved. 
It consists of a vast multitude of cells arranged, as is so commonly the case amongst: 
recent ferns, in interrupted columns running parallel with the vascular axis. These 
cells, which in the perpendicular sections appear to be nearly cubical, are about *0025 
in diameter. Plate LIV. fig. 36 is an enlarged representation of three columns of them 
as they appear in vertical sections. Plate LIV. fig. 29, h , shows how large a portion of 
the bark is occupied by this tissue ; but as we approach the periphery we find that its 
cells gradually become more elongated vertically, as shown in the enlarged figure 37, 
and gradually pass into the outer prosenchymatous layer (k), a few of the cells of which 
are seen in the longitudinal section fig. 38, which is drawn to the same scale as 
figs. 36 Sc 37. At the outer surface the prosenchymatous cells have only a diameter of 
from -00083 to *0012. Closely associated with the stems just described are considerable 
numbers of smaller ones of various dimensions, including mere twigs, like that repre- 
sented in Plate LV. fig. 40. The structure in all these smaller stems is so exactly 
identical with the large ones in every respect, save in the more cylindrical form and in 
the shape of the vascular bundle, that, even had we no direct proof of the fact, there 
could be no doubt as to their being portions of the same plant. Plate LVI. fig. 39 
represents one of the larger examples of this form. 
The central vascular bundle (a) exhibits a crescentic section with incurved angles and 
with three slight tooth-like projections in the interior of the concave margin. When I 
first called attention to these stems, I had not ascertained the relation of the form just 
described to that with the hour-glass bundle (Plate LV. fig. 28). Hence I proposed 
