ANTS AND PLANT-STRUCTURE 403 



calyces, is common all along the Amazon, both on 

 the river banks and in marshy inland sites ; and 

 solitary trees of it are often seen standing out above 

 the Cacao plantations. T. Schomburgkii, Benth., a 

 smaller tree, grows in the same way on the Upper 

 Orinoco and Casiquiari. These trees, as well as 

 the other arborescent Polygonese, have slender 

 elongated tubular branches, often geniculate.at the 

 leaf-nodes, and nearly always with perforations, like 

 pinholes, just within the stipule of each leaf, which 

 are the sallyports of the garrison, whose sentinels 

 are besides always pacing up and down the main 

 trunk, as the incautious traveller finds to his cost 

 when, invited by the smoothness of the bark, he 

 ventures to lean his back against a Tachi tree. 

 I suspect that the remote progenitors of these 

 ants have at first sheltered in the ocrea (sheathing 

 stipule) which is so characteristic a feature of the 

 Polygoneae ; but, having found the wood soft and 

 thin and the pith easy to scoop. out, have made 

 their more secure abode within the stem and 

 branches. 



Some Tachi trees seem as if they were actually 

 trying to run away from the ever-encroaching ants. 

 Coccoloba parimensis, Benth., found by Schomburgk 

 in British Guayana and by myself on the river 

 Uaupes, is an arbuscle with a stem 15 teet long, 

 that tapers upwards and arches over so as finally 

 to touch the ground, the ants all the while hollow- 

 ing it out, as it stretches away apparently in the 

 hopeless attempt to escape their invasion. Some 

 slender Coccolobas climb high into the adjacent 

 trees, not by twining but by crooking their branches 

 and thereby hoisting themselves up ; others arc 



