DR. D. H. SCOTT ON BOTRYCHIOXYLON PARADOXUM. 383 
Diehotomy of the stem is now known to have occurred quite commonly in the 
Zygopterideze. I have myself recorded it in Ankyropteris corrugata (Scott, '08, p. 918) 
(Pl. 40. fig. 19, here). Cases have since been described by Dr. Gordon in Diplolabis Rómeri 
and Metaclepsydropsis duplex (Gordon, '11!, p. 720, and 11?, p. 173). In both plants the 
branching is described as a true or equal dichotomy, but in JMetaclepsydropsis a small 
stele was once observed, just above a petiole-trace departure, which the author thinks 
may indicate that unequal dichotomy also occurred. This observation suggests the 
possible co-existence of dichotomy and axillary branching in the same plant, but the 
evidence is too incomplete to allow of further speculation. At any rate, equal dichotomy 
occurred in Botrychioxylon paradoxum in the only case in which branching of the stem 
has been observed. 
OTHER SPECIMENS. 
Among some sections in my possession, originally belonging to Williamson, but not 
included in his collection, are three containing a small fern-stem. One of them is labelled 
in Williamson's handwriting: “Allied to Rlachiopteris| corrugata,” the latter being, of 
course, the plant now known as Ankyropteris corrugata. The speeimen was found and 
eut by Mr. Lomax, and came from Dulesgate. The sections are numbered 204-206 in 
my collection. "There seems to be no doubt that the stem is the same throughout, but 
in one of the sections (206) the preservation is very much better than in the other two, 
The best section is shown in Pl. 40. fig. 17, and a portion in Pl. 40. fig. 18. The outer 
part of the stem is imperfect, but much of the cortex is preserved. There is a circular 
stele 1:5 mm. in diameter, and at some distance from it is alarge leaf-trace, the 
tangential length of which (1:6 mm.) somewhat exceeds the diameter of the stele. The 
structure of the stele appears to be essentially the same as in the type specimen of 
Botrychioxylon paradoxum. There is a small “ mixed pith,” in which the tracheides are 
more conspicuous than the parenchyma, and the rest of the wood is made up of radially 
seriated elements, giving the same impression of secondary development as the wood of 
the type. There is more indication of medullary rays than we usually find in the latter, 
though the broadest apparent ray is of a different nature, as it seems to contain 
tracheides and, no doubt, is an extension of the internal xylem, connected with some 
appendage. The cortex has practically the same uniform structure as in our plant. The 
inner cells here also are flattened tangentially. 
The leaf-trace has a rather peculiar structure (Pl. 40. fig. 18). There are short 
antennæ at the ends of the xylem ; the protoxylem groups presumably lay on the Fco 
outer side of the antennz; there is no sign of any "i filament : forming a periphe 
loop, though the thickness of the section renders a negative conclusion abc 
uncertain. The rest of the xylem has an unusually irregular form. The E y n i 
Median band (“apolar”) appears to have been originally — ai ula ob cs 
more than a single row of large tracheides; to this, other "e € : M 
unequally in different parts, some of them, to all appearances, by me , 
i a portion of its xylem- 
in fact, we appear to have here a case of a leaf-trace which owes a p 4i 
