981 DR. D. H. SCOTT ON BOTRYCHIOXYLON PARADOXUM. 
development to secondary growth, just as in the supposed leaf-trace of the type, though 
not to the same extent. A diarch root accompanies the stem. 
On the whole, I think this specimen may best be provisionally referred to Botry- 
chiozylom paradoxum, though the characters available are not enough to strictly 
establish specific identity. 
I have also five sections (Nos. 1164-1168) of a second Dulesgate specimen, which 
seems to have some relation to our plant. The preservation is poor, and no leaf-trace or 
petiole is shown. The stele, which varies much in form in the different sections, owing 
partly to differences of preservation, is from 1-1:5 mm. in diameter; the natural form 
appears to have been nearly circular. It has a ‘mixed pith” which runs out into 
conspicuous prolongations containing tracheides, very similar to the internal “ proto- 
xylem rays ” of Ankyropteris Grayi ; they are more developed than in A. corrugata or 
the Botrychioxylon type specimen. The elements of the peripheral zone of wood show 
some degree of radial seriation, though less regular than in Botrychioxylon itself. At 
one point I detected what appeared to be cambium (thin-walled tabular cells) at the 
outer border of the wood, so that some secondary increase took place. The cortex 
agrees with that of Botrychioxylon, and diarch roots are present. 
I do not consider the evidence sufficient to justify a reference of this specimen to 
Botrychioxylon paradoxum, especially as the wood is not so typically secondary as in the 
type. It may prove to be of interest as a transitional form, but at present its relations 
are obscure. 
AFFINITIES. 
When I first examined Botrychiorylon I was impressed by its resemblance to the 
stem of the plant which we now call Ankyropteris corrugata. Evidently Williamson 
had the same idea when he labelled his Dulesgate specimen : ** Allied to Rachiopteris 
corrugata.” At one time I was inclined to go further, and felt some doubt whether the 
new stem might not, after all, be a peculiar condition or a special part of Ankyropteris 
corrugata itself. "The idea suggested itself that Botrychioxylon might be the rhizome, 
while the typical 4. corrugata was the aerial stem ; but this hypothesis does not account 
for the facts, for roots are borne freely on both stems. The points of resemblance 
between our plant and 4. corrugata are: the “ mixed pith ” (internal xylem), the mode 
of emission of the leaf-trace, the dichotomous branching, the presence of secondary wood 
in the stem (only occasional in A. corrugata), the diarch roots, with periderm and 
occasional secondary thickening of the wood. 
The occurrence of secondary wood in A. corrugata seemed at first a striking 
coincidence ; I no longer attach much importance to this, for the same thing has now 
been found to occur elsewhere—for example, in Metaclepsydropsis duplex, in which 
the small branch observed by Dr. Gordon has, as he points out, à Botrychioxylon 
structure (Gordon, *11?). Occasional radial seriation of the xylem is met with ™ 
other stems of the group. The characteristic point in Botrychioxylon is the fact that 
the secondary wood extends all through the stem, so far as the specimen shows, and 
completely replaces the primary peripheral xylem-zone. Nothing like this has been 
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