OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
691 
convex form, and its canal (a") has, in like manner, ceased to be a mere superficial 
groove. But we further observe that the small bundle ( x ) also seen in fig. 35 A has 
now moved away from the larger secondary bundle (aa) with which it was so closely 
associated in the last figure. I think I discover a similar bundle at x 1 in corresponding 
association with the twin secondary bundle ( aa ), to the left of the figure. The several 
vacant spaces ( g ) in this figure indicate areas from which extensions of the inner- 
most cortical parenchyma investing the vascular bundles of the larger petioles have 
disappeared. The masses of the parenchyma of the middle bark (A) are continuous 
with the common investing cortex of the petiole. 
In fig. 35 C, which is a third section of the same specimen, but made at a point yet 
a little higher up in the petiole, we find all the cellular tissues of the bark much more 
homogeneous than in fig. 35 B. The central bundle (a) and its two branches ( aa , aa) 
retain nearly the same relative positions as before. The small bundle (x 1 ) is not very 
clearly seen, but its fellow on the opposite side (x") is now very conspicuous. In a 
section made a little above the last, but which I have not deemed it necessary to figure, 
the bundle x 1 is seen moved still nearer to the periphery. 
Plate LVI. fig. 35 D represents the next section in the ascending order, and is im- 
portant to us. The various structures of this section correspond closely with those of 
fig. 35 C ; but it will be observed that at k, k, k, k we have a broad trifid line of con- 
densed prosenchyma enclosing the two areas of the middle cortex, within which are 
the two secondary bundles (aa, aa), and the left-hand one of these three divergent lines 
again subdivides in like manner to enclose the small ternary bundle (x"). It is sufficiently 
obvious that these dark bands consist of similar tissues to those constituting the 
periphery of the sections fig. 35 A, B, and C, and indicate that along these lines we are 
approaching the peripheral surface, or that, in other words, the rachis is here about to 
subdivide into two secondary rachides (aa, aa) and one ternary one (x"). Still further 
light is thrown upon this matter by another section made still higher up in the petiole, 
and represented in Plate LVI. fig. 35 E. We now find the two secondary bundles 
(aa, aa) not only moved much further away from the central hour-glass, from which 
they are separated by an enlarged mass of the middle cortical parenchyma, but they 
appear as if they were entering two secondary petioles which project from the primary 
one like two horns (y, y). But since these horns are chiefly composed of the prosen- 
chyma of the outermost bark, we have no absolute proof whether they actually repre- 
sent two separate secondary petioles, or mere longitudinal ridges of one secondary 
one. But that the former is the case is almost certain, because we see at k' the 
triangular line of small prosenchymatous cells, such as we find near the surface of the 
outermost bark, and which, I think, clearly indicates the approaching division of the 
stem into three distinct branches — a primary one and two secondary ones, as intimated 
in the description of fig. 35 D. 
Unfortunately we do not possess any further sections of this most interesting speci- 
men, hence we cannot trace the ultimate condition of these secondary branches. The 
MDCCCLXXIV. 5 A 
