Yapp . — Two Malayan ‘ Myrmecophilous ’ Ferns . 189 
The stem has a dorsiventral structure, being roughly semi- 
circular in cross-section, except near the apex, where it is 
more nearly circular. The lower surface, however, is often 
by no means flat, as it has to adapt itself to irregularities of 
the substratum. 
The numerous dark-brown roots are confined to the lower 
surface, and appear to be developed irregularly. 
The leaves arise in regular acropetal succession 1 on the 
upper surface of the rhizome, and have a distichous arrange- 
ment, the members of one longitudinal series alternating with 
those of the other. The petioles are articulated upon large, 
more or less conical processes of the rhizome, which are 
usually directed forwards, i. e. towards the apex of the stem 
(Fig. 23). These conical projections or leaf-cushions are, 
especially on the main stem, often flattened antero-posteriorly. 
They are closely set together (two consecutive leaves of one 
longitudinal series being rarely more than 1-7 cm. apart, and 
usually less), and are separated from each other by transverse 
furrows on the stem. The surface of the rhizome thus 
presents a very rough and irregular appearance, broken up 
as it is and bristling with these conical leaf-cushions, which 
persist after the fall of the leaf (Figs. 3 and 19). 
The branching of the rhizome is, as in all Polypodiaceae 2 , 
monopodial. Lateral branches are given off from both sides 
of the main stem with great regularity (Fig. 6), each branch 
arising opposite to one of the leaf-cushions of its own side. 
The branches originating in this way are closely set together, 
and as they themselves give rise to secondary or tertiary 
branches in a similar manner, whenever space and other 
conditions allow of this, and these branches frequently creep 
over the older parts of the rhizome which come in their way, 
the final result is a compact, tangled mass of interlacing 
branches, so tightly packed as to form practically one solid 
1 At least the leaf-cushions ( vide infra ) are developed regularly, though many 
of them, especially those on the smaller branches, have apparently never borne 
leaves. 
2 Campbell (’95), p. 321. 
