388 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



however, distinguished from all other known glands by definite characters 

 which may, with reasonable certainty, be regarded as special adaptations for 

 the ants' benefit, such as greater size, longer duration, richness in albumen, and 

 easy detachment when touched. Moreover, they lack power of secretion, at 

 least in the later stages of their development. Of special significance in this 

 connection is the fact that quite similar corpuscles occur in the moraceous 

 genus Cccropia and the acanthaceous genus Thunbcrgia and are also asso- 

 ciated with protective ants. The like has never been observed in connection 

 with other plants. In addition to these corpuscles, a nectary situated at the 

 base of the leaf -stalk yields a fluid rich in sugar. 8 



In addition to the ant acacias of eastern Mexico and Central 

 America mentioned above, several beautiful and striking species have 

 been discovered, and two or three species supposed to be identical 

 with them have proved to be distinct. On the shore of Manzanillo 

 Bay, State of Colima, Mexico, a species remarkable for its broad 

 polished, mahogany-colored thorns was collected about the year 1837 

 by Dr. Richard B. Hinds, R. N., surgeon of H. M. S. Sulphur, which 

 was described by Bentham in 1842, and named Acacia hindsii in 

 honor of its discoverer. 9 On plate 8 is shown a figure of this species, 

 collected in the same locality as Doctor Hinds's original specimen. 

 Its thorns have been likened to an inverted military chapeau in 

 shape. This may be called the broad-thorn of Mexico. Closely allied 

 to it is the more recently described Acacia bursaria Schenck of Gua- 

 temala, with still broader thorns. Contrasting with these species in 

 its polished light-colored V-shaped thorns, but resembling them in 

 the form of its curved pods, is Acacia tepicana (pi. 9) from Acapo- 

 neta, Tepic. Two other handsome species are Acacia collinsii (pi. 

 10) from Chiapas, southern Mexico, and Acacia nelsonii (pi. 11) 

 from the vicinity of Acapulco, the first remarkable for its polished, 

 dark-colored, twisted thorns, the second with pale-colored horns 

 shaped like a crescent moon. Last of all comes the beautiful Acacia 

 cookii from Alta Verapaz, Guatemala, with globose heads of flowers 

 (pi. 12) and remarkably long dehiscent pods (pi. 13), very different 

 from all species hitherto described. 



The various species of ant acacias, though resembling one another 

 in the possession of extrafloral nectar glands, apical food bodies, 

 and certain other features, form several distinct natural groups, as 

 shown in figure 4, based chiefly upon the form of their seed pods. In 

 the first group (a), which I have called the " Spine pods," the fruits 

 are inflated, thin-shelled, indehiscent pods terminating in a slen- 

 der sharp spine 10 and containing two rows of seeds {a') embedded in 

 a sweetish yellow edible pulp. In the second group (b) the pods are 

 not spine-tipped nor indehiscent, but split open along two sutures like 



8 Schimper, Pflanzen-Geographie pp. 154-155. 1898. 

 Acacia hindsii Bentham, Lond. .Tourn. Bot. 1. 504. 1842. 



10 To this group belongs Acacia cornigera, characterized by Hermann in bis Paradisi 

 Batavi Prodromus (1689) as Acacia americana cornigera Miquis in spinam abeuntibus. 



