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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, geniculate
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