ANTS AND PLANT-STRUCTURE 393 



ants, for it is a very common thing all through the 

 order of Melastomes. In species which have the 

 leaves of each pair nearly equal, it is usual to see 

 some of the smaller ones saccate and others alto- 

 gether esaccate on the same plant. [I have often 

 examined half-grown plants and have seen that sacs 

 begin to be developed (by inheritance] long before 

 any ants touch them, but that when the sacs are 

 taken possession of by ants they speedily became 

 much enlarged.] 



Seeing, then, how the sacs on the leaves have 

 originated, and what purpose they serve, it is plain 

 that a species of Tococa, like T. planifolia, inhabit- 

 ing the very river's brink, and liable to be com- 

 pletely submerged for several months of every year, 

 could never serve as a permanent residence for ants, 

 nor consequently have any character impressed on 

 it by their merely temporary sojourn ; even if their 

 instinct did not teach them to avoid it altogether, 

 as they actually seem to do ; whereas the species of 

 Tococa growing far enough inland to maintain their 

 heads above water even at the height of flood are 

 thereby fitted to be permanently inhabited, and are 

 consequently never destitute of saccate leaves, nor at 

 any season of the year clear of ants ; as I have 

 r .ison to know from the many desperate struggles 

 I have had with those pugnacious little creatures 

 when breaking up their homes for the sake of 

 specimens. 



In one species (hb. 3477) with seven -ribbed 

 leaves, growing by the Rio Negro near the mouth 

 of the Casiquiari, the leaves on some plants have a 

 small distorted sac at the base inhabited by ants, 

 and on others are nearly all esaccate ; and I noted 



