INSECTS IN RELATION TO PLANTS 



273 



with special reference to their use by ants, though thi- 

 gratuitous ami improbable assumption. 



Belt found several species of Acacia in Nicaragua and the 

 Amazon valley which have large hollow stipular thorns, in- 

 habited by ants of the genus Pscm1i>inynna. The ants enter 

 by boring a hole near the apex of a thorn (Fig. 264, s). The 

 plant affords the ants food as well as shelter, for glands (g) 



FIG. 265. 



FIG. 266. 



Portion of young stem of Cecropia adenopus, Cccropia adenofius. Por- 



showing internodal pits, a and b. Natural size. 



tion of a stem, split so as 



Figures 265-267 are from Schimper's Pflanzen- to show internodal cham- 



gfograpjnt. 



bers and the intervening 

 septa perforated by ants. 



at the bases of the petioles secrete a sugary fluid, while many 

 of the leaflets are tipped with small egg-shaped or pear-shaped 

 appendages (b) known as " Belt's bodies," which are rich in 

 albumin, fall off easily at a touch, and are eaten by the ants. 

 These ants drive away the leaf-cutting species, incidentally 

 protecting the tree in which they live. 

 19 



