Ch. XII.] THE BULL'S-HORX THORN AXT. 221 



plants. Ants of many kinds were numerous ; but none 

 of them took to the thorns for shelter, nor the glands 

 and fruit-like bodies for food ; for, as I have already 

 mentioned, the species that attend on the thorns are not 

 found in the forest. The leaf- cutting ants attacked the 

 young plants, and defoliated them ; but I have never 

 seen any of the trees out on the savannahs that are 

 guarded by the Pseudomyrma touched by them, and have 

 no doubt the acacia is protected from them, by its 

 little warriors. The thorns, when they are first de- 

 veloped, are soft, and filled with a sweetish, pulpy 

 substance ; so that the ant, when it makes an entrance 

 into them, finds its new house full of food. It hollows 

 this out, leaving only the hardened shell of the thorn. 

 Strange to say, this treatment seems to favour the 

 development of the thorn, as it increases in size, bulging 

 out towards the base ; whilst in my plants that were not 

 touched by the ants, the thorns turned yellow and dried 

 up into dead but persistent prickles. I am not sure, how- 

 ever, that this may not have been due to the habitat of 



/ 



the plant not suiting it. 



These ants seem to lead the happiest of existences. 

 Protected by their stings, they fear no foe. Habitations 

 full of food are provided for them to commence house- 

 keeping with ; and cups of nectar and luscious fruits 

 await them every day. But there is a reverse to the 

 picture. In the dry season on the plains, the acacias 

 cease to grow. No young leaves are produced, and the 

 old glands do not secrete honey. Then want and hunger 

 overtake the ants that have revelled in luxury all the 

 wet season ; many of the thorns are depopulated, and 

 only a few ants live through the season of scarcity. As 



