Yapp. — Two Malayan 1 My rmecophilous ' Ferns . 201 
rows of leaf-cushions (across cc in Fig. 20). The slightly 
sinuous course of the ventral gallery is shown by its interrup- 
tion at various points. Three of the vertical galleries with 
their forward diverticula are .also shown. 
The galleries communicate with the exterior by means of 
little passages tunnelled by the ants through the outer tissues 
of the stem. Fig. 5 is a photograph of a transverse section 
through one of these excavations. It will be noticed that the 
internal edges are irregular, and show signs of having been 
gnawed by the ants, while the long processes so characteristic 
of the naturally formed galleries are quite absent. The 
external openings of these tunnels are usually situated on the 
ventral surface of the rhizome, a little below the apices of 
small branches (ct. Fig. 1 5). Shallow pits may also occasion- 
ally be found in similar positions. These pits are evidently 
of the nature of wounds, as the epidermis which should cover 
them is missing, while the adjacent tissues are usually coloured 
brown, and are often contracted as if evaporation of water 
had taken place from the wounded surface. It seems prob- 
able that the pits are really the beginnings of tunnels to 
connect the galleries with the exterior. If this is so, it would 
appear to be usual for subsequent boring operations, as well 
as the original ones, to be conducted from the outside. The 
apical regions of the stem are probably selected by the ants 
because the tissues there are more easily excavated than are 
those of the older and tougher parts. 
B. Root. Adventitious roots are given off at fairly frequent 
intervals from the ventral meshes of the vascular cylinder of 
the stem. They commence just below the growing point and 
develop by means of a single, three-sided apical cell h The 
developing root passes obliquely forwards through the cortex, 
and emerges from the stem some little distance in front of its 
point of origin. Van Tieghem and Douliot 2 have pointed 
out that this cortical part of the ‘ root-stele ’ possesses in 
reality the structure of a stem-stele and not that of a root. 
This is the case also in P. carnosum , the general arrangement 
1 Cf. Bower (’89), p 309. 2 Van Tieghem and Douliot (’88), p. 533. 
P 
