4 io NOTES OF A BOTANIST CHAP. 



are the primary attraction to the ants, which are 

 always of one species and sting virulently. 



I find that I had myself given a short account of 

 these ant-infested plants of both hemispheres in my 

 volume on Nahtral Selection and Tropical Nature 

 (p. 284), in which I refer to Mr. Forbes's observa- 

 tions, and also to those of the late Mr. Belt on the 

 Bull's- Horn Acacia, which has the thorns in a young 

 state filled with a sweetish pulpy substance which at 

 first serves as food for the ants, while later on they 

 are supplied by honey-glands upon all the leaves. 

 He also notices and figures in his Naturalist in 



O 



Nicaragua (p. 223) the leaves of one of the 

 Melastomse with swollen petioles, and he states 

 that, besides the small ants always infesting them, he 

 noticed, several times, some dark-coloured Aphides. 

 He also suggests that these small virulently-stinging 

 ants are of use to the plants by guarding them 

 from leaf-eating enemies such as caterpillars, snails, 

 and even herbivorous mammals, but above all 

 from the omnipresent Sauba or leaf- cutting ant, 

 which he declares he observed to be much afraid of 

 these small species. 



I think the facts that have now been observed in 

 both the western and eastern tropics are really 

 sufficient to enable us to understand the probable 

 origin of the various remarkable structures that 

 have been developed in many different groups of 

 plants and are utilised by ants. There is clearly 

 ' utility " on both sides. The ants obtain dwellings, 

 protection from floods, a safe shelter for their eggs 

 and larvae, and a portion of their food in some 

 cases perhaps all --from the plant they inhabit; 

 while the plant derives protection to its foliage, 



