Maslen. — The Relation of Root to Stem in Catamites . 69 
son and Scott have shown that in the stem-branches of Catamites the pith 
terminates inwards in a narrow neck, by which it is continuous with 
the pith of the stem 1 , and Williamson long ago accounted for the in- 
sertion of the medullary casts of large branches on their stems by means 
of a narrow neck, by the narrowing of the pith 2 . Our Fig. 6 shows that 
the narrowing of the pith inwards also takes place in the roots. Judging 
from this section, however, and comparing our Fig. 6 with the figures of 
stem-branches given by Williamson and Scott, it appears that in the roots 
the narrowing is more gradual than in the stems. Comparison of stem and 
root branches which are cut approximately at the same distance from the 
centre of the main axis on which they are borne, but so as to avoid the 
narrow neck connecting them, shows that the stem-branches have a rela- 
tively larger medulla. Compare our Figs. 2, 3, and 4, and Williamson 
and Scott’s Figs. 5 and 6. 
It is well known, however, that specimens of Astromyelon vary greatly 
in the relative size of the pith, which may consist of very few cells indeed, 
so that they can hardly be identified, or it may be relatively large. This 
extreme variation in size of the medulla is not found in the roots which 
arise directly on the stems and with which we are here specially concerned, 
but only in the smaller specimens. Of these there are many scattered 
through our slides, and they doubtless result from the branching of the 
larger roots, all of which agree in the possession of a well-developed pith. 
Fig. 6 also shows the connexion of the primary and secondary xylem 
of the main axis with those of the root. 
Figs. 7 and 8, Plate II (slides 5 and 7 M) are made from sections 
cut from the same specimen as Fig. 6, but they do not pass through the 
same root. 
The section from which P'ig. 7 is taken is cut longitudinally, and it 
passes into the pith of the stem. The figure shows a medullary ray (w.r.), 
and one of the infra-nodal organs ( i.n.o .). Just above the level of the 
latter, part of one of the nodal diaphragms is preserved {n. d.), and in a line 
with this a leaf-trace bundle can be seen in the section. The leaf-trace 
can hardly be made out in the photograph, although easily seen in the 
section ; its position is indicated at /. t. A root (r.) is shown, and its centre 
is about on a level with the leaf-trace bundle and the nodal diaphragm. 
Fig. 8 shows the same root as the last, but it is cut nearer its origin, 
just above an infra-nodal organ (i.n.o.). In both of these cases, as well as 
in Fig. 6, the central part of the pith has disappeared. There is some 
evidence in these cases that the disappearance is due to fungal action. 
The usual persistence of the pith in Astromyelon was one of the 
1 Loc. cit., PI. LXXX, Fig. 22. 
2 See Organization of the Fossil Plants of the Coal Measures, Part IX, 1878, Phil. Trans., 
PI. XXI, Fig. 30 and description of the same. 
