196 Yapp . — Two Malayan i Myrmecophiloas ’ Ferns . 
Dorsally, along the median line, there runs a single vascular 
bundle, a little thicker than the rest, in a slightly sinuous 
course. On either side of this, in two alternating longitudinal 
rows, are the large foliar gaps. These are oblong in shape, 
and about 11-12 mm. long, by 5-6 mm. wide (d. Fig. 35). 
On either side of each foliar gap, two vertical steles are 
given off, one from the hinder corner and the other about 
half-way along the gap. These branch and anastomose with 
each other and with the steles from the other side of the 
gap to form a network extending up into the leaf-cushion 
and arching over the gap, completely roofing it in except 
in front. A horizontal section through a leaf-cushion thus 
shows a horseshoe-shaped arrangement of bundles (with the 
open part pointing forwards) passing up towards the petiole 
(Fig. 18). Each foliar bundle given off from the central 
dorsal stele usually branches into two. One branch forms 
the anterior bundle (on the inner side) of one leaf-trace, and 
the other the posterior bundle of the next leaf-trace on the 
other side of the middle line (a. Fig. 35). Sometimes, how- 
ever, these two bundles may arise separately from the dorsal 
stele. The consecutive foliar gaps of one longitudinal series 
are separated by a single transverse row of small meshes 
{b. Fig. 35). 
Laterally the vascular cylinder is composed of small poly- 
gonal meshes, about 4-5 mm. long, and not quite so broad. 
Its continuity is interrupted opposite each foliar gap of the 
same side by a large gap corresponding to the origin of 
a lateral branch ( c . Fig. 35). The meshes bounding this 
gap are continuous with those forming the cylinder of the 
branch. 
Ventrally the meshes are similar to the lateral ones. At 
irregular intervals, either from the side of a mesh or from 
a point of anastomosis, a stele is given off which passes 
obliquely downwards and forwards to a root. 
The connexion between the vascular system and the 
galleries will be described later. 
The individual stele is of the bicollateral type, and need 
