198 A NATURALIST IN BORNEO 



growths as those of P. carnosum. In P. carnosum the 

 branching of the rhizome is very extensive, and the 

 branches arise very close together, so that the final 

 result is a close tangled mass of interlacing branches, 

 so tightly packed as to form practically one solid 

 mass which embraces the branch of the tree on which 

 it fgrows. From the upper surface of the rhizome 

 spring the leaves or fronds, and the stems of these 

 are articulated to the rhizome by means of conical 

 projections or leaf-cushions, but it must be noted 

 that a great many of these leaf-cushions do not bear 

 any fronds at all. If a cross-section be taken through 

 a rhizome a number of hollow spaces in the ground- 

 tissue will be seen ; these are the ant-galleries, and if 

 they be traced up towards the apex of the rhizome, it 

 will be seen that they are replaced in this the younger 

 part of the rhizome by a fragile tissue made up of 

 large, thin-walled cells which are filled with water. 

 These cells disintegrate gradually as the rhizome 

 grows forward, and the space formerly occupied by 

 them becomes an ant-gallery. The system of 

 galleries consists of a large central ventral gallery 

 running right along the rhizome and giving off alter- 

 nately on either side lateral galleries to the branches 

 of the rhizome, and a dorsal series of chambers 

 leading into the leaf-cushions. Now though these 

 galleries originate from the breaking-down of thin, 

 water-containing cells, which of course once occupied 

 the spaces now given up to galleries, they are 

 increased in size by the ants which inhabit them 

 nibbling away at their walls ; moreover, they com- 

 municate with the exterior air by means of holes 

 gnawed by the ants, and generally opening on the 



