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OBSERVATIONS ON THE CENTRAL AMERICAN ACACIA 



ANTS. 



By William Morton Wheelek, Ph.D., Boston. Mass. 



The critics who have recently assailed and even demolished 

 many of the brilHant theories bequeathed to us b\- the eminent 

 biologists of the latter part of the nineteenth century, have not 

 overlooked the theory of myrmecophilous plants. As originally 

 promulgated by Belt and Delpino in 1874 and elaborated by 

 Beccari, Huth, Fritz Müller, Schimper, and others, this 

 theory holds that a number of plants, mainly tropical, are pro- 

 tected from their enemies by a body-guard of aggressive ants, 

 and that the plants have been able to enlist the services of these 

 insects b\' furnishing them with suitable dwellings in the cavities 

 of the stems, leaf-petioIcs, or thorns, and an unfailing supply of 

 sweet liquid food secreted by the extrafloral nectaries, or of 

 solid food in the form of special bodies containing nutritious oils 

 and Proteids. The classical cases which were conceived to place 

 this theory on a firm foundation are the East Indian rubiaceous 

 epiphytes of the genera Hydnophytutn and Myrmecodia, the 

 peculiar neotropical trees of the genus Cecropia, and a group of 

 large-thorned acacias peculiar to Central America and Mexico. 

 Other famous cases often cited in this connection are the hollow- 

 stemmed neotropical trees of the genus Triplaris and the shrubs 

 of the genus Cordia. 



Treub (1888) and Rettig (1904) have proved that the 

 peculiar cavities in the pseudobulbs of the epiphxtic R\ibiaceiE 

 have a physiological origin and function (¡uitc independent of 

 the ants, which later come to inhabit them, and voN IHERING 

 (1907) and Fiebrig (1909) have shown that the Cecropias have 

 no more need of the Aztecas, which rcgulaily ocruj^y their hollow 

 limbs and feed on their Miilkrian bodies, than (log> havr oí tluir 



