RELATIONS OF ANTS TO VASCULAR PLANTS. 



35 



The foregoing facts, it must be confessed, do not furnish a very 

 solid foundation for the myrmecophily hypothesis that has been built 

 upon them. At most they disclose considerable adaptability on the 

 part of the ants, and a rather dubious or clumsy counter adaptation 

 on the part of the plants. But the authors who would convince us 

 that there is a definite symbiosis between such very different organisms, 

 advance as their chevau.v de bataillc a few cases in which certain exqui- 

 sitely arboreal ants live in a definite association with certain plants that 

 present unusual structural characters. . Such are the association of the 

 Brazilian Aztcca nmclleri with Cccropia adenopus, that of the Malayan 

 Iridomyrmex inynnecodicc with Myrmecodia and Hydnophytuui and 

 that of Pscudoinynna with Acacia in Central and with Triplaris in 

 South America. We must therefore consider these cases in somewhat 

 greater detail. 



The relations of Azteca muelleri to Cecropia adenopus have been 

 studied by Fritz Muller (1876, 1880), Schimper (1888), and von 

 Ihering (1891, 1907). The tree 

 known as the " imbauba " or " im- 

 bauva " belongs to the Urticacae 

 and is very slender and candelabra- 

 shaped, growing to a height of 12- 

 15 m. It is most abundant along 

 the Brazilian littoral. The trunk 

 and branches are hollow except at 

 the nodes, where there are thin 

 transverse septa (Fig. 172). The 

 sap is colorless, not milky nor rub- 

 ber-containing, as stated by some 

 authors. The crown of foliage is 

 meagre and consists of large, paim- 

 ately lobed leaves. At some time 

 of its life each node bears a leaf, the 

 long petiole of which has at its base 

 a hairy cushion, known as the 

 trichilium (Figs. 172^, 173*), in 

 which the yellow Miillerian bodies 

 (in} are imbedded. The cavities 

 almost without exception tenanted 

 forates the septa and thus causes all the internodal cavities to 

 communicate with one another, both in the trunk and branches. 

 The ants do not, however, live in the smallest, still actively growing 

 twigs. The just-fecundated queen enters the branches while the tree 



FIG. 175. Hydnophytuui nwntanitin 

 of Siam, showing pseudobulb in sec- 

 tion. (Forel.) 



Of 



by 



older and larger trees are 

 Azteca nmclleri, which per- 



21 



