OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
19 
the parent stem not having been perfectly accomplished. Nevertheless there are indi- 
cations that such a separation is in progress. Thus we see at h a mass of cellular tissue 
separating the vascular masses on either hand of it ; not only so, but we discover at the 
peripheries of three such vascular masses a tendency towards that convergence of the 
outer extremities of the newly forming vessels of each primary wedge which has been 
already described and illustrated by fig. 32, g. The largest of the vessels in this branch 
does not exceed '0025 in diameter. 
On glancing at fig. 33 the observer is strongly disposed to conclude that the mean- 
dering vessels radiating outwards from the parent stem to the half-formed branch were 
equally derived from the two wedges, c', c" ; but I believe that, primarily at least, this is 
not the case. I have already pointed out that in the lowest of the three sections 
(fig. 32) the aberrant vessels (x) unmistakably proceed from the w r edge c, being separated 
from d by the radiating extension of the inner bark (h!). I have another transverse section 
of the specimen from which the above three were made, which exhibits a second and 
similar branch, but which has been so bent in the plane of the section that, though the 
main stem is intersected transversely, the section cuts through the branch longitudinally. 
In this case the branch certainly proceeds solely from one of the neighbouring primary 
wedges. In all these sections the vessels of the secondary branches are much smaller 
than those of the parent stem. It is not impossible that as the branch develops, both 
the contiguous primary wedges may contribute some vascular elements towards its for- 
mation, as appears to be indicated by fig. 33. 
In fig. 33 the peculiar cellular tissue which I have termed pseudo-cambial forms an 
almost continuous semicircular belt around that peripheral upper portion of the branch 
in which the vascular laminEe have assumed their normal radiating order. But in fig. 34, 
on the other hand, it has begun to concentrate itself into masses at the extremities of 
the incipient primary vascular wedges, as in the matured stem. This is especially the 
case at the four points g , g, g , g. It is obvious that these several points represent a cor- 
responding number of incipient primary vascular wedges. 
Having ascertained these facts, I turned with some interest to the well-known stems 
of the Bignoniaceae, to see how far the orientation of their lateral branches corresponded 
with what I have just described. In these plants there is a distinct medulla, and the 
lateral twigs are given off in pairs. When this is about to take place, two of the four 
woody wedges constituting the Maltese cross exhibited by a transverse section of the 
stem become much broader than the other two, and a prolongation of the pith passes 
outwards through the centre of each of these enlarged wedges, and carries along with it 
an investing cylinder chiefly composed of sclerenchyma. Thus each branch springs 
from the centre of a woody wedge, and not from its sides, as in my fossil plant. It fol- 
lows that in the JBignonice the areas occupied by the centripetal prolongations of the 
cortex separating the four arms of the cross take no’part in the formation of the branch ; 
whereas we have seen that in my fossil this area is largely concerned in its formation. 
In one point, however, there is a resemblance between the two cases. In the very 
D 2 
