Yapp . — Two Malayan ‘ Myrmecophilous ’ Ferns . 1 9 1 
usually confined to the main stem and the largest and most 
vigorous branches. Both kinds are glabrous, pinnatisect with 
a terminal lobe, lamina glaucous and sub-coriaceous, petiole, 
rachis and midribs dark brown. 
Sterile fronds 2-9 cm. long (including petiole), 1 *5-4*5 cm. 
wide, with one terminal lobe and 1-3 pairs of lateral segments. 
Segments shortly-oblong to oblong-ovate, obtuse, somewhat 
contracted at the base, margin entire or repand. Veins 
immersed except the midribs, which are more prominent on 
the upper than the lower surface. The lateral veins branch 
and anastomose freely, forming on each side of the midrib 
two or three series of areolae enclosing free veinlets with 
swollen terminations. The costal series of areolae is the 
largest (Fig. 45). Petiole short, 2*5 cm. at most, somewhat 
semicircular in cross-section (the flatter side facing apex of 
stem), usually slightly winged almost to the base. 
Fertile fronds often 30 cm. or more long (including petiole), 
and 4 or more cm. wide, with one terminal lobe and 15-25 
pairs of lateral segments, the lower sterile and similar to 
those of the sterile fronds, the upper fertile, narrowly oblong, 
obtuse, bearing 2-1 2 marginal lobes, each of which bears one 
deeply sunken sorus. The size of the segments diminishes 
slightly from base to apex. 
The sori are circular, and commence in slight depressions 
on the lower surface of the marginal lobes of the leaf-segment. 
During development, the depressions become deeper and 
deeper until they assume a cup or bucket shape. Meanwhile, 
the soriferous lobes bend gradually upwards, until they are 
completely reflexed upon the upper (ventral) surface of the 
leaf. In order to accommodate the depth of the sorus-cups, 
the margin of the leaf is also bent upwards. Various stages 
in this process are shown diagrammatically in Fig. 42, a , b, e, d. 
As is usual in the Polypodiaceae, the sori contain sporangia in 
all stages of development. When mature, the sporangia are 
long-stalked, but in a young sorus the stalks do not elongate 
until the sorus-cup is almost fully formed. At this stage the 
mouth of the cup is oblong, but as the sporangia mature and 
