696 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
appearance of obliquity. The base of the branch is embedded in a sheath of 
secondary xylem, which is not perfectly continuous with the normal wood upon 
which it is superposed. The peculiarity of this case lies in the want of connection 
between the base of the branch and the primary xylem of the parent root. As we 
have no other sections of the specimen, we cannot be absolutely certain that the 
actual base of the branch may not have passed obliquely inwards, and attached 
itself to the protoxylem of the main axis in another plane. The structure, however, 
shows no sign of such obliquity, and there is every appearance that the abrupt inner 
termination of the branch is its real base. If so, the branch must either have been 
an adventitious one, formed after secondary growth had already made some progress, 
or else it may have been a normal branch tc begin with, which became separated 
from its place of origin by the intercalation of secondary wood. An analogous 
process is well known to happen in the case of “sleeping buds” in some recent trees, 
such as the beech. 
We have examined a longitudinal section, from a different specimen, which shows 
essentially the same peculiarities. 
The following conclusions may be drawn from the study of branched specimens. 
1. The roots of Calamites, like those of the recent Equiseta and of vascular plants 
generally, branched endogenously. 
2. The minute, pithless rootlets were, in some cases, borne on parent roots of the 
ordinary ‘‘ Astromyelon” type, with a distinct pith. 
3. In exceptional cases it appears that the base of the branch-root was separated 
from the primary xylem of the main axis by a zone of secondary wood. 
Conclusion. 
A general survey of the numerous specimens which we have investigated, shows 
conclusively that there is no sharp distinction between the small pithless rootlets 
and the large medullate roots. The extreme types are connected by an unbroken 
series of intermediate forms. As regards the number of primary xylem-strands, 
every number, from 2 up to 14, is represented ; while we also find larger roots with 
16 and 25 strands. As regards the size of the pith we find it of all dimensions, from 
a microscopic group of two or three cells, up to a diameter of nearly 2 centims. ; nor 
is there any break in the series. We will only call attention here to two of the 
intermediate forms. In a previous memoir* a root is figured which at first sight one 
might take for a pithless rootlet. We have re-examined the specimen, and find that 
it has a perfectly distinct pith, about seven cells in diameter, surrounded by seven 
groups of primary xylem, which form an almost continuous ring. The root shown in 
photograph 6 has a slightly larger pith, eight to ten cells in diameter; its structure is 
probably hexarch, but as the primary xylem-strands are well separated from one another, 
* “Organization,” Part XII., Plate 28, fig. 6 (C.N. 1809). 
