142 



THE FACTORS 



[Part 1 



ants, or rather they would be so if they were not kept at a distance 

 by their relatives which form the defensive army. They show such 

 a preference for the foliage of Cecropia, that, at Blumenau, Fritz Mullet 

 and I found every one of the uninhabited trees, which are rare, had its 

 leaves bitten down to the midrib, whereas not a single tree with r 

 protective army of ants showed a trace of such injury. Only duriiu 

 the lowest winter temperatures is an inhabited tree exposed to its enemies 

 for the protective ants are much more sensitive to cold than are thd 



parasol-ants^. Other ani- 

 mals, as it appears, are noij 

 kept off Caterpillars occui 

 on the tree, though withou 

 doing much damage, anc 

 the sloth exhibits such ; 

 preference for it, as to re, 

 ceive the same name (im| 

 bauba) in Brazil. None of it: 

 enemies, however, can com-i 

 pare with the parasol-ant:| 

 in destructiveness. 



A closer investigation 

 proves that the imbauba-trei| 

 provides its guests with ; 

 dwelling and food. The ceni 

 tre of the stem is traverser 

 by a transversely divide( 

 cavity, which increases ii 

 calibre from below upward 

 like a funnel, correspondinj 

 to the increasing thicknesj 

 of the growing apex, so tha' 

 the uppermost chambers i 

 the stem are larger tha 

 those represented in ou 

 illustration (Fig. 77). Thj 

 cavity, and therefore th 

 dwelling-place of the ants, in spite of its great utility, is not an adaptatio 

 to the guests ; it represents rather a feature that is common to man 

 other plants, and may be explained on the mechanical principle c 

 construction as being the method of producing the greatest resistanc 

 to bending with the least expenditure of material. The dwelling existe 

 before the symbiosis. It is otherwise with the entrances to it. Her 



^ Alf. MoUer, op. cit., p. 82. 



11 



Fig. 77. Cecropia adenopus. Portion of a young stem 

 split longitudinally. Central hollow with septa per- 

 forated by the ants, and structures made by them. Natural 

 size. 



