Polycycly. 223 
of Pteris, while by far the most important function of the internal 
vascular system is to supply the deep lateral folds of the petiolar 
system, it is quite possible that in origin it may be an elaboration of 
the leaf-gap margin, as in Matonia. Evidence from the structure 
of the young plants is needed to settle this question. 
Dictyostelic Cases. 
The vascular system of the Cyatheaceae (Fig. 68), the typical 
tree-ferns, is a polycyclic dictyostele, though the internal vascular 
system is of distinctly different type from most of the forms hitherto 
considered. The main vascular system consists of a very wide 
dictyostele, the band-shaped meristeles with their sheaths of 
sclerenchyma, as seen in transverse section, extending from the 
edge of one leaf-gap to that of the next, near the periphery of the 
bulky stem. The curved leaf-trace rapidly breaks up in the base 
of the petiole into a number of separate nearly isodiametric 
strands, kidney-shaped in cross-section. The outline of the 
whole system of petiolar strands has practically the same form 
as in the two species of Pteris just described, but the free 
edges of the curve are bent in abaxially (Fig. 69, A) as in the 
A B 
a 
Fig. 69. Cvathea Bninonis. A.—Transverse section of base of petiole 
showing vascular curve with deep lateral folds and incurved ends, consisting 
of a number of small kidney-shaped meristeles a — a, b — b, c—c, strands to 
which internal accessory strands of the stem have joined. 
F. — Leaf-trace seen from within, a , b, c, internal accessory strands joining 
certain strands of leaf-trace curve. From Gwynne-Vaughan. 
young Matonia. In addition to the primary system of the stem 
there are a number of isodiametric strands scattered in the pith. 
In Cyathea Bninonis (Fig. 69), one of the simplest types of the genus, 
four of these internal strands run up into each leaf-gap, two joining 
onto the two leaf-trace strands situated at the bottom of the deep 
lateral folds on each side (a) while the other two bifurcate, one branch 
of each (c) joining the strands at the adaxial outer corners of the 
lateral folds, the others (b) joining the strands forming the incurved 
free edges of the trace (Gwynne-Vaughan ’03). Here then we have 
