66 



MY LIFE 



[Chap. 



beneficial to the plant itself. That is, I suppose, an incontro- 

 vertible axiom. Odoriferous glands, especially if imbedded 

 in the leaf, act as a protection against leaf-cutting ants, and 

 (to some extent) also against catterpillars. I can remember 

 no instance of seeing insects attracted to a plant, to aid in its 

 fertilization, or for any other purpose, by their presence. The 

 glands on which some insects feed are (so far as I know) 

 always exposed, either in the shape of cups on the petioles, 

 involucres &c., or of hairs with dilated and hollow bases, 

 and of sessile or stalked cysts, on the leaves, petioles, 

 pedicels &c. ; and the secretion is either tasteless or slightly 

 sweet, but inodorous — to our senses at least. 



"Trees with aromatic leaves abound in the plains of 

 equatorial America. Those which have the aromatic (and 

 often resinous) secretion imbedded in distinct cysts include 

 all Myrtacea, Myrsinege, Sanydeae, and many Euphorbiaceae, 

 Compositse etc. The leaves of very few of these are, when 

 growing, ever touched by leaf-cutting ants. In the few cases, 

 however, where the secretion is slightly but pleasantly bitter, 

 and wholesome, as in the Orange, the leaves are quite to their 

 taste. At a farm house on the Trombetas ^ I was shown 

 orange-trees which had been entirely denuded in a single 

 night by Sauba ants. Various expedients are resorted to by 

 the inhabitants of Sauba-infested lands to protect their fruit- 

 trees, such as a small moat, kept constantly filled with water, 

 around each tree ; or wrapping the base of the trunk with 

 cotton kept soaked with andiroba oil, etc. 



[Note. — Leaf-cutters in the vicinity of man work chiefly 

 by night, taught doubtless by painful experience of his vicious 

 propensity to interfere with their operations. But in the 

 depths of the forest I have often caught them at work, some 

 up a tree cutting off leaves and even slender young branches, 

 others on the ground sawing them up and carrying them off. 

 When at San Carlos,^ I one day went into the forest to 

 gather a Securidaca (woody Polygaleous twiner) I had seen 

 coming into flower a few weeks before. I found it in full 



^ A northern tributary of the Amazon above Santarem. 



2 The first village in Venezuela on the Upper Rio Negro. — A. R. W» 



