432 BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 



The ants are incapable of assisting- in pollination, for the plant is 

 dioecious and the pulverulent pollen seems to indicate that it is ane- 

 mophilous. By causing the disappearance of the medullary tissue and 

 thus rendering the branches lighter, the ants may facilitate the devel- 

 opment of the tree, and consequently its elevation above the top of 

 other trees, an arrangement especially favorable for the transportation 

 of pollen by the wind. 



The Glerodendrum Jistulosum is a verbenaceous plant visited and 

 inhabited by ants. Its straight stem, about a meter in height, has 

 internodes that all appear enlarged. Each enlargement has at its 

 summit, just below the insertion of the leaf of the internode above (one 

 of the two opposite leaves of each internode having aborted), an orifice 

 bounded by a projecting rim. The ants are attracted to the surface of 

 the plant by little nectaries situated on the inferior surface of the 

 leaves near the median nervure. It is not yet known if these inter- 

 nodes with their apical openings are absolutely constant features. 

 Beccari supposes that the irritation produced by ants may cause a 

 notable increase in the internodes and in the size of their cavity. The 

 openings may have been in the first place the work of ants, though the 

 cavities do not intercommunicate, for the ants that inhabit this Glero- 

 dendron belong to an eminently perforating genus {Golobopsis). It 

 would appear, however, that at the present time these openings are 

 produced without the intervention of ants, that a lesion has become 

 hereditary. The services rendered by ants to the Glerodendron are, 

 first, a protection against herbivora. Delpino saw a plant of this 

 genus (G. fragans) defended by armies of ants as soon as anyone 

 attempted to gather its flowers. Then these myrmecophilous features 

 may assist the G. jistulosum in its struggle for existence with neighbor- 

 ing species. The irritation produced by the ants may perhaps cause a 

 notable increase in the internodes and their more effective lignification, 

 the subherbaceous plant being thus enabled to struggle with more 

 advantage against rival species in the midst of tropical vegetation 

 largely of a ligneous character. If this is the case we may suppose that 

 primitively individuals inhabited by ants survived in preference to 

 those which were not so inhabited, and natural selection consequently 

 fixed these myrmecophilous features. The swelling of the internodes 

 and the perforations, at first accidental characters, became normal. 



Everyone has heard of the curious Nepenthes, commonly reputed to be 

 carnivorous plants. The Nepenthes bicalcarata is one of the most inter- 

 esting species of the genus and is to-clay cultivated in the hothouses of 

 Europe. Its climbing stems ascend trees to a height of from 10 to 15 

 meters. Its leaves are terminated by ascidia or pitchers, having the 

 well-known form peculiar to the genus, which has caused the plant to 

 be regarded as one of the most carnivorous of vegetables. These 

 pitchers are so markedly dimorphic that they might be supposed to 

 belong to two different species. The leaves of the upper part of the 



