374 DR. D. H. SCOTT ON BOTRYCHIOXYLON PARADOXUM. 
details, such as the sculpture of the tracheides. The first sections were sent me on 
January 10th, 1902. The long delay in publishing a full description of the specimen, 
which Mr. Lomax detected as a “new stem,” is due, among other causes, to certain 
difficulties of interpretation, which even now are not completely surmounted. 
I have eight sections in all (Nos. 2459-2466 in my collection), of which six are transverse 
and two are longitudinal. Three of the transverse sections (2459-2461) are from the lower 
part of the specimen; then come the longitudinal sections (2462 and 2463), passing through 
the bifurcation of the stem ; the remaining transverse sections (2464-2466) are from the 
upper part of the specimen and are cut through the more vertical of the two branches, 
The two branches into which the stem divides are approximately equal in size (Pl. 39. 
fig. 10); the fact that the branching, so far as we are able to judge, was by dichotomy 
is an important one and a striking point of agreement with the stems of Ankyropteris 
corrugata (Pl. 40. fig. 19), Diplolabis Rimeri, and Metaclepsydropsis duplex. 
The stem bears appendages of three kinds: leaves, aphlebize, and adventitious roots. 
No petiole is shown in actual connection with the axis, but there is no doubt, as will be 
further explained below, that the petiole seen in the upper transverse sections belongs to 
the plant (Pl. 37. fig. 4). Aphlebi:e, comparable to those of other Zygopteridew, and 
adventitious roots are seen in continuity with the stem at various places. 
The stem does not diminish in thickness, within the limits of the specimen. In the 
lowest section the diameter is about 9 mm.; in the section next above the dichotomy 
the one branch shown measures about 1 cm. ; in the following sections the stem is 
incomplete, but appears to keep about the same size. On the other hand, the stele is 
much smaller above the dichotomy. In the lowest section it measures 3:2x 2'7 mm. 
In that next below the dichotomy (2461) the dimensions are 3 x 4'4 mm., the increase in 
one direction being partly due to obliquity of section; above the dichotomy (section 2464) 
the stele of the vertical branch is only 1:7 mm. in diameter, and in the next higher 
section only about 1 mm., but here the condition is not quite normal. The structure of 
the stem is simple. The stele, where not affected by the emission of appendages, has an 
approximately circular transverse section (Pl. 38. fig. 6). Its structure is described in 
the next part of the paper. Beyond the stele is a very wide cortex of almost uniform 
structure throughout. In the lower sections (Pl. 37. figs. 1 & 2 and PI. 38. fig. 5) the 
inner cells are tangentially compressed, owing probably to secondary growth of the stele, 
but in the upper part, where this growth is less in amount, there is scarcely any 
differentiation (Pl. 38. fig. 6). The absence of mechanical tissues suggests that the stem 
was a rhizome. On the outside is a definite layer of periderm, several cells in thickness 
(PL. 37. fig. 8). 
STRUCTURE OF THE STELE. 
The structure of the stele is shown, in transverse section, in the photographs (PL 
figs. * & 2, Pl. 38. figs. 5 & 7, and Pl. 89. fig. 8). The main features—the central * mixed 
pith," the broad zone of radially seriated wood, and the somewhat narrow phloem-region 
on the outside—are evident at the first glance. In the lower sections (Pl. 37. figs. 1 . d 
and Pl, 38, fig. 5) the central tissue has an elongated form and appears compressed, 
