Anatomy of Solenostelic Ferns . 713 
stele in D. aculeata is more than twice as broad as the dorsal 
region. In consequence of this the enclosed ground-tissue is 
displaced so as to occupy an excentric position near the 
dorsal surface (Fig. 19). The extra breadth of the ventral 
half of the solenostele is entirely due to the increased amount 
of xylem present in that region, because the sheath of phloem 
and pericycle is of approximately even thickness through- 
out, both on the inside and on the outside of the stele 
(Fig. 20). No definite protophloem is to be made out on 
the inside of the stele, although it forms a fairly distinct 
layer on the outside. The absence of an internal proto- 
phloem is, however, sometimes to be observed even in 
typical solenosteles, e. g. Lindsaya retusa. The leaf-trace 
departs from the narrow dorsal region of the solenostele 
as a single curved strand with its concavity directed toward 
the median dorsiventral plane of the rhizome. In passing 
outwards it gradually loses its curvature, and in the free 
petiole has the form of an equilateral triangle with rounded 
angles and sides ; the xylem-strand, however, still remains 
V-shaped. The leaf-gap is very small and is closed up at 
the same time as the acroscopic margin of the leaf-trace is 
set free. 
In Davallia pinnata the habit of the stem and the insertion 
of the leaves is exactly the same as in D. aculeata. The appear- 
ance presented by the vascular system also, at least in sections 
taken just below a leaf-insertion, is very similar in both. It 
has at these points the form of a hollow vascular cylinder, the 
wall of which is very much broader in the ventral region than 
it is in the dorsal, and the ground-tissue enclosed within the 
stele is displaced, as in D. aculeata , so as to lie excentrically 
near the dorsal side (Fig. 21). On the other hand, the extra 
breadth of the ventral half of the vascular ring in D. pinnata 
is not entirely due to the xylem alone as it was in D. aculeata. 
The internal phloem also takes part in its production, there 
being a much greater quantity of this tissue on the ventral 
side of the enclosed ground-tissue than on the dorsal (Fig. 22). 
The anatomy of this plant has already been described by 
3 C 2 
