Friends and Foes 261 



grow not singly, but in branching clusters— make any 

 forest where it abounds absolutely impassable. 



The buffalo thorn, or bull's horn acacia, is interesting 

 in another way. Its trunk and branches are beset by 

 strong thorns two or three inches long and as sharp as 

 needles, which grow in pairs, and are shaped just like 

 horns. But as if this were not enough to insure its 

 safety, the tree maintains as well a standing army, which 

 keeps off all aggressors, large and small, at least during 

 the wet season, for then every thorn is tenanted by ants, 

 which rush out and sting severely any animal venturing to 

 touch the tree. 



Caterpillars, which might make their way between the 

 thorns without injury, have no chance against the ants, 

 and even their own rapacious relations, the leaf-cutting 

 ants, are completely baffled. 



The ants of the buffalo thorn are not to be found in 

 the forest, or indeed anywhere except on this particular 

 acacia, which belongs especially to the dry plains or savan- 

 nahs of Central America. When the "horns" are first 

 put forth they are filled with a soft, sweetish pulp, which 

 the ants hollow out, burrowing between the partition 

 which separates them, and thus making a single dwelling 

 of each pair. The thorns do not suffer in any way from 

 this treatment, and continue to grow until they have 

 reached their full size. 



But the ants do not frequent the trees for the sake of 

 comfortable lodgings merely. They want, and find, food 

 as well. At the base of each pair of young leaflets there 

 is a gland, which contains a liquid something like honey; 

 and besides this, the young leaves bear what are described 

 as "minute golden pears," small, sweet protuberances, 



