Boodle.—Anatomy of the Hymenophyllaceae. 473 
scattered protoxylem-elements, and, in the case illustrated, 
one small island and two bridges of metaxylem. The phloem 
is continuous, but still scanty on the upper side. A drawing 
of the young stage of the petiole, cut through its lower 
region, is seen in Fig. 25. The large cells (pc') are developing 
tracheides of the metaxylem arc, and there are four groups 
of fully developed tracheides (px) representing the protoxylem. 
The two lower ones will, judging by their position, abut on 
the arms of the metaxylem. The position of the protoxylem- 
elements appears to be variable, but, at any rate, several of 
them lie immersed in the parenchyma. In the mature petiole 
the partly collapsed protoxylem-elements are not very 
noticeable, and were overlooked by Prantl in T. speciosum , 
Willd., in which he includes certain forms from Ireland and 
Madeira falling under T. radicans in Hooker and Baker’s 
Synopsis. Prantl describes and figures diagrammatically 
( 1 . c., Fig. 51) the protoxylem as occupying the two lateral 
angles of the triangular xylem. 
As in previous cases, the base of the petiole is more stem¬ 
like than the upper part, in having a closed ring of xylem 
with intefnal protoxylem. 
The nodal structure is illustrated diagrammatically by 
Figs. 28-32. Fig. 28 shows the relative positions of the 
axillary branch (br), the petiole (pet) and the main stem in 
longitudinal section, the vascular tissue being shown lighter 
than the cortex. The stele of the branch is attached to the 
leaf-trace just below the point where the latter curves sharply 
out into the petiole 1 . This is not universally the case, 
however, as in one node of this species the stele of the branch 
was attached directly to that of the main stem, a short 
distance above the attachment of the leaf-trace. The next 
three diagrams represent transverse sections through the nodal 
region of the same species. In Fig. 29 the leaf-trace and the 
steles of the stem and axillary branch are all distinct. Fig. 30 
shows leaf-trace and stele of axillary branch fused, but their 
1 This is described by Prantl ( 1 . c.), but his diagram (of another species), Fig. 63, 
does not make it clear. 
