310 THE BIOLOGY OF FLOWERING PLANTS 



imbauba, or trumpet tree, or in hollow stipules, e.g. in 

 Acacia sphcerocephala. They gather albuminoid food bodies 

 modified glands, from the leaf tips of the Acacia ; on the 

 upper surface of the petiole of Cecropia, hidden in a mat of 

 hairs, they find similar succulent, stalked glands, rich in 

 proteins and fats. It was first suggested by Belt (1874) that 

 the imbauba profited by harbouring the ants, which live 

 in its stem hollows and feed on the glands. He observed 

 that trees, which, for some reason had no inhabitants, were 

 stripped of leaves, while the inhabited trees were immune. 

 He supposed that the food bodies were borne in relation to 

 the needs of the ants ; and that these had easy entrance to 

 the stem cavity provided for them by a thin place situated 

 above the insertion of each leaf, which is readily gnawed 

 through. The hypothesis of a close inter-relation between 

 ant and plant was elaborated by many subsequent investi- 

 gators, of whom the chief was Schimper, in whose book an 

 account of the subject will be found. More recently doubts 

 have been cast on the use of the ant army to the plant and 

 on the idea that any structure in the plant is really related 

 to the attraction of these guests. We may mention the 

 work of Ihering (1907), Ule (1906), and Bailey (1922, 1923), 

 and the critical summing up by Neger. The drift of the 

 criticism is that the clever ant simply makes use of any 

 feature in a plant which may be made to serve its need for 

 shelter or food. As regards the plant it receives little or no 

 advantage from the ant. " Cecropia adenopus can get on 

 as well without Azteca as a dog without a flea." The 

 hollow stem or stipule is a common feature of all sorts of 

 plants which have no relations with ants. The thin place 

 through which the ant bites its way is a mechanical result 

 of the pressure of the axillary bud — though this does not 

 explain the openings into the hollow which are formed with- 

 out the aid of the ant in some plants of the eastern tropics, 

 such as Humboldtia laurifolia, and Ficus incequalis. Even 

 food bodies are found in some plants which have no relations 

 with ants, as in the pearl glands of species of Vitis. Leaf- 

 cutter ants are unknown in the eastern tropics where, never- 



