128 Chapters in Modern Botany CHAP. 



and similar cases. But precise knowledge of the meaning 

 of this partnership was not attained till 1874, when Belt, 

 the naturalist of Nicaragua, and Delpino, an Italian 

 botanist, cleared up the whole matter. Let us quote Belt's 

 account a of his discovery : " The thorns of the bulPs- 

 horn Acacia are hollow, and are tenanted by ants that 

 make a small hole for their entrance and exit near one 

 end of the thorn, and also burrow through the partition 

 that separates the two horns, so that one entrance serves 

 for both. Here they rear their young, and in the wet 

 season every one of the thorns is tenanted, and hundreds 

 of ants are to be seen running about, especially over the 

 younger leaves. If one of them be touched, or a branch 

 shaken, the little ants (Pseudomyrma bicolor) swarm out 

 from the hollow thorns, and attack the aggressor with jaws 

 and sting. They sting severely, raising a little white lump 

 that does not disappear in less than twenty-four hours. 

 They form a most efficient standing army for the plant, 

 which prevents not only. the mammalia from browsing on 

 the leaves, but delivers it from the attacks of a much more 

 dangerous enemy the leaf-cutting ant. For these services 

 the ants are not only securely housed by the plant, but are 

 provided with a bountiful supply of food, and to secure 

 their attendance at the right time and place, the food is so 

 arranged and distributed as to effect that object with 

 wonderful perfection." There is a sweet gland at the 

 base of each pair of leaflets on the bipinnate leaf, and a 

 little yellow pear-like body at the end of each small division 

 of the compound leaf which is carried off when ripe. The 

 young thorns are soft and filled with sweet pulp, so that 

 the ant finds its house full of food. As it hollows this out, 

 the thorn increases in size and bulges out towards the 

 base. 



1 The Naturalist in Nicaragua. Lond. 1874. 



