XXIV ANTS AND PLANT-STRUCTURE 405 
None of these fistulose trees and shrubs have 
any sacs or swellings 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 Rupprechtia Janiesoni, 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 
