Yapp. — Two Malayan \ Myrmecophilous ’ Ferns. 197 
not be described in great detail. It is of small size, and is 
elliptical in cross-section. The xylem, as in many Polypo- 
diaceae 1 , consists entirely of tracheides, and is somewhat 
scanty in amount. Between the phloem and the endodermis 
(which has the usual thickened radial walls) is the pericycle. 
This is composed of one or two layers of relatively large cells, 
which are superposed upon those of the endodermis (vide 
Fig. 33). This probably indicates that we are here dealing 
with a so-called ‘double endodermis’ and not a true peri- 
cycle 2 . 
The bundle is surrounded by a dark-brown sheath com- 
posed of a single layer of cortical cells, with very much 
thickened inner walls (s. Fig. 33). These walls are traversed 
by numerous large radial pits. 
Origin of the galleries . The growing point of the stem is 
fleshy and presents a blunt, somewhat rounded appearance. 
There is nothing to indicate the exact position of the actual 
apex. Several attempts were made, by means of serial sections, 
both freehand and microtome, to determine whether a single 
apical cell is present or not, but without success. 
Immediately behind the growing point a transverse section 
of the stem is very uniform in appearance, consisting, with 
the exception of the epidermis and the procambial strands, 
of very thin-walled parenchymatous cells, more or less equal 
in size. About 1 or 2- mm. from the apex, however, the cells 
in certain definite areas may be seen to increase in size at 
a greater rate than do the surrounding cells. This differen- 
tiation becomes more marked the greater the distance from 
the growing point, for not only do these cells themselves 
increase enormously in size, without undergoing much, if any, 
division, but the cells surrounding them begin to divide by 
radial 3 and also to some extent by tangential walls. An early 
stage in the differentiation is shown in Fig. 8 and a much 
later one in Fig. 9. The large-celled tissue thus formed is 
surrounded when mature by a belt, several layers deep, of 
1 De Bary (’ 84 ), p. 344. 2 Cf. Van Tieghem (’88), p. 404. 
3 Radial as regards these large-celled areas. 
