382 DR. D. H. SCOTT ON BOTRYCHIOXYLON PARADOXUM. 
quite the ordinary Botryopteridean* type. Roots, however, also occur in which the 
diarch xylem-plate is increased by the addition of secondary tissue. Roots with 
secondary growth are so rare in plants of this affinity that it is essential to find strict 
proof that the organs in question really belonged to our plant. This I was able to 
prove in the case of the large root (1°7 mm. in diameter) shown in Pl. 40. fig. 16. In 
Pl. 37. fig. 4 two large branching outgrowths are seen springing from the stem, one on 
either side of the petiole. One of these outgrowths ends in a body (7.), which can be 
traced through the next two sections, becomes free, and appears as a manifest root in 
the section figured (Pl. 40. fig. 16). The xylem-plate is incomplete, but was evidently 
diarch ; two or more layers of secondary xylem-elements have been added on either side 
of the primary plate; they appear to be interrupted opposite the protoxylem; the outer 
secondary tracheides are large, suggesting a possible funetion as a water-reservoir. In 
the outer part of the cortex the cells show a radial seriation indicating that a periderm 
had been formed. Periderm in roots is not unknown among Zygopteride:, it is 
commonly present in the larger roots of Ankyropteris corrugata. I have also found 
secondary wood well developed at the base of a root of this species T, but such cases 
are rare. It is interesting to recall that Mr. Boodle found abundant secondary wood at 
the base of the root in Botrychium Lunaria, and also, though only to a small extent, in 
roots of Ophioglossum vulgatum (Boodle, '99, pp. 386—388, pl. 20. figs. 9 & 14). 
The branched outgrowths already referred to (Pl. 37. fig. 4) are curious structures: 
they are closely associated with aphlebize, and at first sight suggest some kind of cauline 
appendage; on closer examination, however, it appears that they are merely branched 
roots: wherever any structure can be made out it agrees with that of a root; the 
associated aphlebize are never in connection with the outgrowth, and can sometimes be 
seen to spring from the stem. In all cases the roots arise close to aphlebise, which may 
have served to protect them when young. 
The root-steles, so far as observed, arise directly from the stele of the stem, without 
any evident relation to the leaf-trace. 
Tur BRANCHING OF THE STEM. 
Little need be added to what has already been said (p. 374). Of the two branches into 
which the stem divides, the vertical one is shown in its full thickness, while the other is 
incomplete (Pl. 39. fig. 10). The stele of the complete branch is 2 mm. in diameter at 
the base, 1'8 mm. higher up. Half the thickness of the other branch is shown; the 
diameter was evidently about the same in both. The branching was thus à dichotomy, 
using the word in the somewhat loose sense which is inevitable in dealing with fossils. 
The petiole shown in Pl. 37. fig. 4 and Pl. 39. figs. 11 & 12 was given off on the side 
opposite the inclined branch, so we might, if it were worth while, speak of the vertical 
branch as axillary. Obviously, however, there are no means of ascertaining whether 
there was any constant relation between the branching and the leaf-insertion. 
* Using the word in Renault’s original comprehensive sense. | + Shown in section 2721 in my collection. 
See 
s Sioa cia 
