306 Friends and Foes 



which is thickly studded with knobs, each ending in a 

 thorn as large and sharp as the bill of a sparrow-hawk. 

 Even the tough hide of the elephant is not proof 

 against the 'jungle nail/ or ' elephant thorn/ an acacia, 

 whose lancet-like spines which frequently grow, not 

 singly, but in branching clusters make any forest 

 where it abounds absolutely impassable. 



The buffalo thorn, or bull's horn acacia, is interest- 

 ing 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 ensure 

 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 barfled. 



The ants of the buffalo thorn are not to be found 

 in the forest, or, indeed, anywhere except on this par- 

 ticular acacia, which belongs especially to the dry 

 plains or savannahs 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, 



