Yapp . — Two Malayan ‘ Myrmecophilous ’ Ferns . 209 
a. Rhizome . Here and there, in a transverse section of the 
stem, occur pit-like depressions, the sides of which are lined 
by the epidermis. From the floors of the pits spring the 
cylindrical stalks of the peltate scales. These stalks are 
composed of a number of elongated cells, with very thick 
brown walls. The cells immediately above the stalk have 
comparatively large lumina, and these pass in all directions 
into the shallow, radially arranged cells of the scale. The radial 
walls of the latter cells are marked with numerous large pits 1 . 
There is no special thick-walled hypoderma. 
The vascular cylinder in this Fern is somewhat flattened 
dorsi-ventrally. In a transverse section of the stem it appears 
as an oval ring of steles (Figs. 24, 25). A semi-diagrammatic 
drawing of a dissection showing the dorsal part of the 
vascular cylinder is seen in Fig. 36. The meshes of the 
network are small and elongated. It is difficult to define the 
actual limits of the foliar gaps, but apparently they are much 
elongated, with pointed ends. The supposed boundaries 
of one of them are indicated in Fig. 36, by the slightly 
thicker steles lying between the points a and b. From the 
edges of this gap numbers of steles are given off, which branch 
and anastomose to form an extensive network (similar in 
appearance to that of the main cylinder) arching over the 
foliar gap behind, but rising more abruptly in front to enter 
the leaf-cushion. Laterally, secondary cylinders are given 
off to the branches, and from the ventral meshes steles pass 
downwards to the roots, much in the same manner as in P. 
car nosum. In fact, the whole vascular cylinder of P. sinuosum 
much resembles that of P. carnositm , if we can imagine the 
latter stretched or pulled out in a longitudinal direction 2 . 
1 Karst en (’95), p. 180, describes the structure of these scales in detail. He 
regards their function as twofold, (i) to protect the stem against excessive trans- 
piration, (2) to collect and temporarily store water during the fall of rain, for the 
subsequent use of the roots. Water is quickly sucked up by the expanded part of 
the scale, but from the structure of the stalk Karsten thinks it unlikely that any 
finds its way directly into the stem. 
2 Boodle (’01, 2nd paper), p. 739, points out that strongly xerophytic conditions 
are likely to conduce to shortening of internodes and decrease of rate of growth in 
stems. Probably the shorter internodes (and therefore the apparently contracted 
