ANTS AND PLANT-STRUCTURE 405 



None of these fistulose trees and shrubs have 

 any sacs or swelling's on the branches, except the 

 leguminous genus Platymiscium, which has the 

 pinnate leaves usually in whorls of three, and the 

 tubular branches sometimes dilated at the leaf- 

 nodes ; so that this genus has almost as much right 

 to be placed in the preceding section as here. 



All the plants above named belong to the eastern 

 side of the Andes and the Amazonian plain ; but 

 when I crossed over to the western side of the 

 Andes I saw a Triplaris in the Red Bark forests 

 of Chimborazo, and Rnpprechtia Jamesoni, Meisn., 

 and a Coccoloba on the inundated savannas of 

 Guayaquil, with just the same long, slender, geni- 

 culate branchlets infested by the same class of 

 ants as their congeners east of the Andes. 



A few other plants with long-drawn-out stems 

 and branches, such as some species of Remijia, may 

 be supposed to owe at least the exaggeration of 

 that feature to the ants which still continue to 

 infest them. 



Nearly all tree-dwelling ants, although in the 

 dry season they may descend to the ground and 

 make their summer-houses there, retain the sacs and 

 tubes above-mentioned as permanent habitations ; 

 and some kinds of ants appear never to reside else- 

 where, at any time of year. The same is probably 

 true also of ants which build nests in trees, of 

 extraneous materials, independent of the growing 

 tissues of the tree itself. There are some ants 

 which apparently must always live aloft ; and the 

 Tococa-dwellers continue to inhabit Tococas where 

 there is never any risk of flood, as in the case of 

 the T. pterocalyx, which grows on wooded ridges 



