ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 8938 
transversely across a branch at some little distance from its actual base, we often find 
a highly peculiar structure, already described and figured in former memoirs.* The 
transverse section of the branch shows no well-defined pith and no clear traces of 
the primary groups of xylem. It consists of a parenchymatous mass, into which 
tracheides penetrate in all directions from the surrounding secondary wood. These 
intruding tracheides describe strange curves, and extend as far as the middle of the 
branch, cutting up the parenchyma into isolated groups.t In fact, in these cases, as 
we trace the branch outwards, its structure, instead of approaching more nearly to 
that of the normal Calamitean stem, becomes more and more anomalous. Such a 
structure is in fact totally different from that of a Calamites or any other known 
stem. From the sections of Mr. Wixp’s specimen we know that no such peculiarities 
are found in a normal branch, at any point, from its base upwards. We believe that 
the true explanation is to be sought in the fact that the remarkable structure in 
question is not a normal one, but is due to the abortion of the branch, and the 
consequent enclosure of its base by the secondary wood of the parent stem. 
We have direct evidence proving that branches became abortive and were enclosed 
by the wood. A good illustration of this is afforded by the radial section already 
mentioned.{ Here the normal pith of the branch can be traced outwards, up to a 
certain point, at which it is suddenly cut off by a layer of secondary wood seen in 
radial section. The section is obviously median, so there can be no doubt that the - 
wood really shuts off the end of the truncated branch. Precisely the same pheno- 
menon is shown in some of the transverse sections (see Plate 80, fig. 22), which pass 
through the median plane of a branch. Here also the parenchymatous pith of the 
branch extends for a certain distance from the base, and is then suddenly cut off 
by a mass of secondary wood, which, in this case, is seen in transverse section. The 
1ine between the pith of the branch and this callus-wood, if we may call it so, is 
nearly straight, or if anything convex towards the interior, so the appearances cannot 
possibly be explained by obliquity of section. We have, in fact, two other sections 
of the same branch, passing one above, the other below, its median plane, and the 
three together prove conclusively that the truncated end is completely shut in by 
secondary wood.§ 
In these, and other similar cases, it is evident that a meristem was formed across 
the pith of the branch, at a certain stage, by which secondary wood was formed, 
completely cutting off the basal portion of the branch from all direct communication 
with the exterior. We can hardly doubt that the free end of the branch was 
previously or simultaneously cast off. It is impossible to say at what stage of 
* See Wituiason, “ Organization,” Part IX., Plate 21, fig. 26. 
+ As shown in C.N. 88, 131*, and other preparations. 
¢ C.N. 97, Winxiauson, “ Organization,” Part IX., Plate 21, fig. 27. 
§ The sections in question are C.N. 133*, 134*, and 135*. From the middle one our figure is drawn. 
Other branches in the same preparations show the same structure. 
