146 



THE FACTORS 



[Part I 



differs neither externally, nor in the nature of the tissues lying within 

 it, from the groove of which it forms the upper extremity. In spite 

 of the absence of a protective army, the ant-free Cecropia proved to 

 be quite uninjured, apparently because the waxy coating of the stem 

 prevented the leaf-cutting ants from climbing. It has indeed been proved 

 experimentally that a waxy coating offers an insuperable obstacle 1 . 



Cecropia adenopus, which probably most 

 of the other species of the genus resemble, 

 represents a higher stage of adaptation than 

 Acacia cornigera and A. sphaerocephala, for 

 it exhibits as adaptations not only the food- 

 bodies, but also the spot that is prepared 

 beforehand to be bored through. In the latter 

 respect Clerodendron fistulosum, discovered by 

 Beccari in Borneo, resembles Cecropia. Other 

 species however have gone a step further, for 

 they have succeeded in forming an opening 

 through the wall of the hollow internode. 

 The causes that lead to the formation of an 

 opening have not yet been explained ; in 

 certain cases it may be the result of a tension, 

 in others perhaps due to the death of the 

 tissues of a circumscribed area. The opening 

 is sometimes narrow, like a slit, so that it 

 has to be widened by the ants, as in Duroia 

 hirsuta, according to Schumann ; sometimes 

 from the first it is more circular and porelike, 

 and thus perfectly fitted for its subsequent use 

 (Fig. 83, 1-3). 



The spontaneous appearance of an opening 

 in the previously intact wall of hollow inter- 

 nodes was first rendered probable by Bower 

 in the case of Humboldtia laurifolia, then 

 by Schumann in several species. I first 

 became fully convinced of its truth in the 

 botanic garden at Buitenzorg, where I ob- 

 served quite free from ants specimens of 

 Humboldtia laurifolia and Triplaris americana, also Ficus inaequalis 2 , 

 hitherto unknown as a myrmecophyte, all with a well-differentiated 

 entrance-aperture at the upper end of most, or of all the internodes. 



1 Schimper, op. cit. p. 66. 



2 But proof is still wanting that it is inhabited by ants in its native habitat. In the 

 Singapore botanic garden most of the specimens were inhabited. 



Fig. 82. Cecropia sp. of the 

 Corcovado Mountains, near Rio de 

 Janeiro. Part of the myrmecophilous 

 stem. Natural size. 



