$86 DR. D. H. SCOTT ON THE HETERANGIUMS 
masses, is less crushed than the stele. The specimens are closely associated 
with those of the 8 form, sometimes appearing in the same sections *. 
The stems vary in size. Williamson's type-stem (specimen 1 ; W. 1915 H) 
measures about 14:5 x 5*5 mm., with wood (badly crushed) about 6 x 2:5 mm. in 
diameter. This is only exceeded in size by one of the 8 stems. Specimen 2 
is about the same size, with a smaller branch. Specimen 24 is a little 
smaller than the first two ; while the obscure specimen 1 a, of which only the 
stele is preserved, must have been fairly minute, the wood only measuring 
about 2:5 x 1:5 mm. 
So far as the erushed state of the tissues allows one to judge, the structure 
of the wood did not differ from that of the specimens already described, 
unless it be that in the æ stems the centrifugal wood of the bundles is some- 
times rather more developed. With one partial exception, to be mentioned 
presently, no secondary wood has been detected. 
The pericycle contains sclerotic groups as in other specimens. The cortex 
is the best-preserved part of the stem, and presents a rather striking appearance 
owing to its strong mechanical construction, the amount of sclerotic tissue 
exceeding anything observed in the other forms (see Pl. 4. figs. 16 & 17, 
and compare with fig. 13 and Pl. 2. Phots. 9, 12, 13, 14). The longitudinal 
sections confirm this (see Williamson’s figures, 1890, pl. 15. figs. 17 & 18, 
and compare fig. 15 here). The sclerotic nests are both large, often exceeding 
1:6 mm. in diameter, and numerous. The outer cells are elongated radially 
to the mass. The hypoderma is well developed, with a preponderance of the 
fibrous tissue, as is usual in young stems. The epidermis is well preserved 
in places. 
Owing to the crushing of the stele the specimens are unfavourable for 
following the course of the leaf-traces, for portions of the wood are often 
mechanically severed from the main mass and may simulate outgoing strands, 
while genuine leaf-traces may be crushed in and become unrecognizable. 
In Williamson’s figured specimen (l. c. fig. 14) the double strand at a may 
probably be a leaf-trace, but there is no proof. On the other hand, the two 
double bundles, a little higher up on the left, certainly constitute a trace. 
They are best shown in a Manchester section (Q. 10) cut just above Williamson's. 
This is altogether a good section, with the wood rather less crushed than 
usual; the leaf-trace is particularly clear (Phot. 15). Whether it is in 
* The known specimens of the a form are as follows: Specimen 1. W. 1915 IT; Q. 10, 
R. 643, R. 657 (transverse); W. 1915 F (longitudinal) from the same stem. la. A smaller 
stem appearing in the four transverse sections, as above. The larger stem, 1, may be taken 
as the type (Williamson, 1890, figs. 14-16, 18). Specimen 2. W. 1885 H*, 1885 HH, 
1915 M*, 1915 N*, 19150; R. 642*; S, 236% (transverse). 2«. A smaller stem occurring 
in the sections marked * above, Specimen 3, W. 1915 E (transverse); W. 1915 I, 1915 K, 
1915 L (longitudinal) probably from the same stem. The order of the sections will be 
mentioned in the text when necessary. 
