XXIV ANTS AND PLANT-STRUCTURE 401 
To this category belong the creeping rhizomes 
of some ferns which are often beaded with globose 
swellings inhabited by ants ; e.g. of Phymatodes 
Scho7nburgkii, J. Sm., a not uncommon fern on shady 
rocks and trees by the Rio Negro. [In a small Poly- 
podium, found by Dr. Jameson on the river Napo, 
the moniliform character of the rhizomes seems to 
have become permanent, for he did not see a single 
specimen wanting it ; but the presence of ants in 
all the swellings revealed the origin of the latter.] 
A curious epiphytal genus of Solanaceae, Marckea, 
whereof I gathered two species on the Rio Negro 
and Uaupes, is singularly affected by ants. The 
stem is reduced to a large tuber — sometimes as big 
as a child's head — and attains that size through the 
agency of ants, who inhabit its hollow interior and 
cover it outwardly with paper of their own manu- 
facture. From the tuber radiate several branches, 
simple or sparingly forked. The leaves are very 
like those of Acnistus a7^boresce7is, save that they 
are verticillate (or at least approxim.ated) in one 
species i^M. ciliata, Benth.) in threes and in the other 
species in fives ; but the large hypocrateriform 
corollas, with a tube 3 inches long, are more like 
those of some Gesnerea. There are perforated 
swellings at the forks of the branches, and some- 
times also at the leaf-nodes, which serve the ants 
as detached apartments. I did not see a single 
plant wanting the basal tuber. 
§ 4. Of Elongated and Fistulose Stems and Branches 
There is an order of plants, whereof several 
genera and species inhabit Equatorial America, and 
VOL. II 2D 
