RELATIONS OF AXTS TO I'ASCULAR PLANTS. 



33 



that the food of the insects is obtained exclusively or even in great 

 part directly from the plants, for, as will be shown in a future chapter, 

 many ants visit plants mainly for the purpose of feeding on the excre- 

 ment of the aphids, coccids, etc. In the Old World the exclusively, 

 or at any rate, very largely arboreal genera are (Ecophylla, Cataulacns. 

 Sima and Polyrhachis, in the New World Azteca, Pseudomynna, 

 Cryptoccrus, Myrmelachista and Allomcrus, and in both hemispheres 

 Dolichodcrus, Camponotus, Cremastogaster and Iridouiyrinc.v. The 

 only forms, however, which are so exclusively arboreal as to show 

 unquestionable structural adaptations to this habit, belong to the genera 

 Azteca, Pseudomynna, Sima and to Colobopsis, a subgenus of Campo- 

 notus. Concerning the habits of Azteca and 

 Pseudomynna Forel (1904) says: 'The 

 species of Azteca show very disparate condi- 

 tions in the castes of the same species. Some- 

 times the head of the female is elongated, 

 sometimes greatly broadened ; and in like man- 

 ner vary the proportions of the large and small 

 workers. Emery was the first to call attention 

 to this fact in his excellent monograph of the 

 genus Azteca [1894^]. I believe that these 

 differences are correlated with differences in 

 habit. Just as the species- of Eciton are the 

 robbers of the soil in the primeval forest and 

 the Atta species are the destroyers of the foliage 

 of the neotropical woods, so the species of 

 Azteca and Pseudomynna are the true monarchs 

 of the trees. To my knowledge, none of the 

 species of Azteca and only one Pseudomynna (P. elegans] nest in 

 the ground. But what a varied arboreal existence is led by these 

 little monkeys among the ants as they climb and scurry about 

 everywhere on the trees ! Some of them build carton nests on the 

 trunks and branches, others nest in great cavities in the trunks ; others 

 (A. hypophylla) nest under the leaves of certain vines with these 

 organs closely applied to the trunks, and close up any openings at the 

 edges of the leaves with carton. Others, again, make use of the cavi- 

 ties of dead branches, while still others nest in the natural medullary 

 cavities of living Cecropia trees or any hollow swellings or spaces in 

 all kinds of plants. Finally Mr. Ule has discovered and described ant- 

 gardens in which grow certain epiphytes that are sown by species of 

 Azteca. Now I believe that the long, narrow head of the female and 

 of the large workers of many members of this genus, as well as that 



FIG. 173 Base of 

 leaf petiole of Cecropia 

 adenopiis. (Schiinper.) 

 t. Trichilium, or hairy 

 cushion in which the 

 Miillerian bodies ( m ) 

 are formed. 



