Yapp . — Two Malayan ‘ Myrmecophilous * Ferns . 203 
fine, delicate reticulum with minute, irregular meshes. The 
appearance of these thickened cell-walls, especially those of 
the outer cortical cells, reminds one forcibly of the tracheidal 
cells in the velamen of an epiphytic orchid 1 . Possibly they 
function in a somewhat similar way, though it must be 
remembered that these cortical cells are living, while the 
velamen tracheides are dead. At all events, the numerous 
and comparatively large thin places between the thickening 
rods would probably greatly facilitate the transport of water, 
which would be of service to the plant, as, being an epiphyte 
with large water-storing capacity, rapid absorption of water 
during rains would be advantageous. The cortical cells them- 
selves also might very well store the water temporarily, until 
the somewhat limited vascular tissue of the root could carry 
off the surplus. 
Apparently neither the piliferous layer nor the very per- 
sistent root-hairs ever possess this thickening network. 
Lateral secondary roots are of frequent occurrence, and are 
developed in two ranks, emerging from the sclerenchymatous 
sheath at the thin places opposite to the two protoxylem 
groups. 
C. Leaf .—Petiole. In transverse section the petiole is seen 
to be slightly winged, and more or less semicircular in shape 
with the flatter side directed towards the apex of the stem 
(Fig. 38). Beneath the epidermis, which has a rather thick 
cuticle, is the usual well-marked hypodermal tissue of thick- 
walled fibrous cells, with pointed ends and no intercellular 
spaces. The outer layers of the hypoderma are coloured 
brown, the inner are colourless and pass over into the larger 
cells of the ordinary petiole parenchyma. At two points, i. e. 
just behind the two wings, the fibrous hypodermal zone is 
interrupted by a thinner- walled spongy tissue (a. Fig. 38). 
Communication is thus established between the stomata, 
which only occur above the spongy tissue, and the inter- 
cellular spaces of the internal parenchyma. This tissue, as is 
often the case in Ferns 2 , extends in two narrow, continuous 
1 Cf. Haberlandt (’ 96 ), p. 201, Fig. 77. 2 Gwynne-Vaughan (’ 01 ), p. 83. 
