Vascular System of Matonia pectinata. 491 
of which is sometimes solid and sometimes in the Lindsay a- phase, with 
occasionally an endodermal rod enclosed in the central phloem. The 
leaf-trace at a short distance from its origin shows in cross-section the 
form of a flat-topped arch (Fig. 23) with the free edges of the xylem 
sometimes merely thickened and sometimes with an incurved hook 
structure, which has been recently shown to be very common in the 
petioles of Ferns with a comparatively simple vascular structure h The 
free edges of the arch are approximated, and the cavity of the arch is 
occupied by ground-tissue in continuity with that of the petiolar cortex 
by an isthmus passing between the free edges. The whole structure 
is much like that of Gleichenia , § Mertensia , and even more closely 
resembles that of L ox soma 1 2 . 
The behaviour of the inner cylinder at the nodes is the same, in 
essentials, as in the plant F, i. e. it becomes attached to the outer cylinder 
dorsally towards the end of the node, just before the end of the departure 
of the wings of the leaf-trace. When the leaf-trace departs symmetrically 
the inner cylinder sends up a broad column between the bases of the arms, 
closing the gap in the outer cylinder and at the same time contributing a 
strand of tracheids to the thickened end of the leaf-trace arm on each side. 
Immediately after the closure of the gap, the inner cylinder again becomes 
free, its internal phloem and endodermis (where present) remaining un- 
affected throughout the node. When the leaf-trace departs to one side 
of the dorsal line and asymmetrically, i. e. with the dorsal arm leaving 
before the lateral one, the connexion of the inner cylinder with the outer 
takes place below the dorsal arm, before the closure of the gap. In 
some cases the junction only takes place (just as is normally the case 
in many of the nodes already described in the young plants) after the 
departure of the leaf-trace is completed. It might be thought that in 
such a case the function of the inner cylinder was confined to closing the 
leaf-gap, as it undoubtedly is in many of the nodes of the younger 
plants, but in this case an actual continuity can be traced between 
the tracheids coming up from the inner cylinder, backwards through the 
thickened edges of the gap, and up the edges of the leaf-trace arms. 
This backwardly running supply of the incurved arms of the trace is, 
as we shall presently see, much more extensively developed in the more 
complex types. 
The next stage of complexity is to be found in one of the ‘ starved ’ 
plants (H), with larger, stouter leaves, a rhizome of 2 mm. and an outer 
stele of 1 mm. diameter — a considerably larger plant than G. 
The inner cylinder is here solenostelic, or sometimes, after the departure 
1 Cf. Boodle (’0 1 B), PL XXXVIII, Fig. 7 ; (’01 A), PI. XX, Fig. 17, PL XXI, Fig. 44. Gvvynne- 
V anghan (’03), Pl. XXXIV, Fig. 25, PL XXXV, Fig. 26. 
2 Gwynne- Vaughan (’01). 
