192 A NATURALIST IN BORNEO 



natural selection should not have brought into exist- 

 ence this power to produce such structures. If the 

 presence of the ants is of advantage to the plants in 

 protecting them from other enemies, so much the 

 better, and perhaps in some myrmecophilous plants 

 the need for this protection has called into being 

 definite ant-harbouring devices. But this does not 

 seem to be so with Myrmecodia and Hydnophytum, for 

 not only has it yet to be shown that they need this 

 protection, but Treub's experiments show, on the con- 

 trary, that without the ants the plants flourish quite 

 well. It is a fact worthy of consideration that in 

 Borneo it is one species of ant which, to the almost 

 entire exclusion of other species, lives in nearly all the 

 myrmecophilous plants ; it is found in the species 

 of Korthalsia, in both genera of myrmecophilous 

 Rubiacece, in Polypodium spp., and in the species of 

 Dischidia. It may also be noted that the same ant is 

 frequently found in the hollowed-out branches and 

 twigs of shrubs not specially adapted for harbouring 

 ants, and we may believe that these tunnels are exca- 

 vated by the ants themselves. It is thus evident that 

 Cremastogaster difformis is a species that habitually lives 

 in any convenient hollow or tunnel that it can find, 

 and, if it cannot find one ready, it will excavate one. 

 The very ubiquity of this ant tells against the view 

 that there is a real symbiosis of ant and plant. In 

 true cases of symbiosis one species of animal lives on 

 or in another species of animal or plant : we do not 

 find one species living on or in half a dozen or more 

 other species, and, failing to find a convenient com- 

 panion, living an independent life. That ants can be and 

 are of immense service to some plants is certain. The 



