388 NOTES OF A BOTANIST 
Ant- Agency in Plant-Structure ; Or the Modi- 
fications in the Structure of Plants which 
have been caused by Ants [by whose long- 
continued Agency they have become Heredi- 
tary and have acquired sufficient Permanence 
to be employed as Botanical Characters]. 
In the forests of the Amazon and Orinoco, and 
elsewhere in Tropical America, there are numerous 
plants belonging to very distinct orders, which have 
singular dilatations of the tissues and membranes, 
in the form of sacs on the leaves, or of hollow fusi- 
form nodes on the petioles or branches (becoming 
tubers on the rhizomes), or of slender inordinately- 
elongated fistulose branches. I have reason to 
believe that all these apparently abnormal structures 
have been originated by ants, and are still sustained 
by them ; so that if their agency were withdrawn, 
the sacs would immediately tend to disappear from 
the leaves, the dilated branches to become cylin- 
drical, and the lengthened branches to contract ; 
[and although the inheritance of structures no longer 
needed might in many cases be maintained for 
thousands of years without sensible declension, I 
suppose that in some it would rapidly subside and 
the leaf or branch revert to its original form]. 
§ I. 0/ Sac- be ajHng Leaves 
These exist chiefly in certain genera of Mela- 
stomes, whereof one (Tococa) is very numerous 
in species and individuals throughout the Amazon 
valley, growing in the form of slender weak bushes, 
8 to 12 feet high, chiefly in that part of the forest 
