3 88 NOTES OF A BOTANIST 



. \XT-AGENCV 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 by them ; so that if their agency were withdrawn, 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. Of Sac-bearing 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, 



to 12 feet high, chiefly in that part of the forest 



