202 Yapp . — Two Malayan ‘ Myrmecophilous ’ Ferns . 
of the stelar tissues as well as the sclerenchymatous sheath 
conforming to the usual structure of a stem-stele in this Fern. 
As the young root emerges from the cortex, it is at first 
covered by a cap formed of the epidermis of the stem. This 
cap finally ruptures, and is left behind as a collar encircling 
the root close to where it emerges from the stem 1 . Fig. 37 
shows a layer of these collar-cells (c) external to the piliferous 
layer of the root. 
The mature root has a diameter of about 1 mm. It 
possesses a diarch xylem plate, containing only a few tra- 
cheides. The one or two central elements of the metaxylem 2 
remain unlignified until quite a late stage (Fig. 34). The 
stele is enclosed in a sclerenchymatous sheath, which, like 
those in the stem, is of a dark-brown colour. It is composed 
for the most part of two or three layers of cortical cells with 
very thick walls and extremely small lumina, while outside 
there is a layer whose inner walls only are thickened. Oppo- 
site to the two protoxylem groups, however, the sheath is 
very much thinner, and consists merely of the thick inner 
wall of one large passage-cell (sometimes there are two such 
cells placed side by side). This thick wall of the passage-cell 
is traversed radially by very large pits. 
The outer cortex consists of about six or seven layers of 
cells, and is bounded by a piliferous layer. The whole, 
including the root-hairs, is stained a yellowish-brown with 
phlobaphene. The cell-walls of the outer cortex are thickened 
in a similar manner to that described for the stem paren- 
chyma, but in the root the thickening bars are much thinner, 
and form a more definite and regular network (Fig. 31). In 
the peripheral part of the cortex the network is comparatively 
coarse, but on travelling radially inwards the network becomes 
finer, and many of the thickening rods still thinner, until in 
the region of the passage cells the walls are covered by a very 
1 Van Tieghem and Douliot, loc. cit., p. 533, describe similar cases in other 
Ferns. 
2 Metaxylem is used here in the same sense as that employed by Boodle (’ 00 ), 
p. 458, i. e. to include all xylem other than protoxylem. 
