The Tropical American Genus Tachigalia Aubl. (Caesalpiniaceae)

Abstract

TACHIGALIAS 225 striking instance of the absence of myrmecodomatia is in the well-collected species, .pubiflora Benth.The works of Bailey? and Bequaert' provide us with the bulk of data on myrmecophily in plants, although only one species of Tachigalia was studied, T. paniculata.Apparently in the immature leaves the initial swelling at the base of the petiole is not induced by insect action but is a "normal hypertrophy" of the leaf-base.This is the first step in a normal process culminating in the establishment of "hollow petioles and rachises of adult sun plants."This natural hollowing-out process, independent of insect work, results in a petiole which may support the heavy pairs of leaflets of the adult plant.However, the usual fate of the normal hypertrophies of the juvenile petioles of seedlings growing in shade is to be attacked by two species of ants.5 Whether this attack is responsible for the petiole and the rachis of the inflorescences being so radically altered in such species as T. formicarum, T. rusbyi, and T. cavipes is not known.It would seem logical, however, to consider this condition to be due in part to the work of insects.From a taxonomic viewpoint Bailey's studies on the single species T. paniculata may serve to suggest the possible sequence of steps involved in the maturation of the leaves of all of the tachigalias.In the juvenile plants of T. paniculata growing in shade the petioles show a distinct basal enlargement (the potential myrmecodomatium) while in older plants exposed leaves show a more fasciated character (cf.loc.cit., fig.1).According to Bailey, the young leaves are widely separated under weak light; when the saplings grow in exposed light the leaves change to a yellow