ANTS AND PLANTS 199 



lower surface of the rhizome. The actual function of 

 these galleries is not quite clear, but their regularity 

 and symmetry is in definite relation to the branches 

 of the rhizome and to the arrangement of the leaf- 

 cushions. The ant which Professor Yapp found in- 

 habiting Polypodium carnosum growing on a mountain 

 in Perak was a new species of Cremastogaster, which 

 has been named after its discoverer. In Sarawak I have 

 found the ubiquitous C. difformis in the galleries of 

 this fern. Professor Yapp believes that the ants are 

 of no service to the ferns, and their presence may be 

 accounted [for in the same way as in Myrmecodia. 

 The galleries are possibly for the aeration of the 

 rhizome. Professor Yapp points out that there are no 

 stomata on the stem, and there are no intercellular 

 spaces in the rhizome tissue. In the absence of these 

 adaptations for gaseous exchange in tissue which is 

 capable of assimilation, there must be a tendency to 

 partial asphyxiation, which however is obviated by 

 the galleries, which function as air-passages. It is also 

 possible that when the hot sun shines on the exposed 

 fern, water vapour condenses on the walls of the 

 galleries and is re-absorbed when the temperature falls. 

 Rain-water also may find its way into the galleries 

 and be absorbed. For my own part I prefer to 

 regard these galleries as produced for the same pur- 

 pose as those which I have alleged for Myrmecodia. 



Finally, we come to those very singular Asclepiads, 

 the species of Dischidia with pitchers, several of which 

 are found in Borneo, though only two appear to have 

 been described. All are epiphytic plants with slender 

 liana-like stems straggling over the branches and twigs 

 of trees on which they grow. In the majority of 



