THE PLANT AS A HOST 35 



bers of ants, and the vigorous little creatures will 

 certainly not allow any other visitors. Thus 

 numbers of small beetles and other insects which 

 happen to be trespassing on the plant are dealt 

 with very effectually. 



The relations of plants and ants are known to 

 be more definitely intimate than in any of the 

 foregoing instances. As long ago as 1688 the old 

 naturalist John Ray observed the frequent occur- 

 rence of ants in the hollow stems of Cecropia 

 palmata and some other South American plants. 

 It was not until the latter part of last century 

 that an understanding of the matter was in any 

 way complete. The actual observations were 

 made in the case of the Bull's Horn Acacia. In 

 this tree it was found that the hollow thorns were 

 inhabited by ants, the insects making a hole for 

 their entrance and exit near one of the thorns. 

 In these little homes they rear their young, and 

 Belt declared that in the wet season every one 

 of the thorns in the trees he examined (in 

 Nicaragua) was inhabited. If any browsing animal 

 should attack the tree, the ants resent the inter- 

 ference with great fury, rushing out to deal with 

 the aggressor with jaws and stings. 



The services rendered to the Acacia go even 

 beyond this. South American forest trees are much 



