430 BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 



Belt succeeded in cultivating this Acacia. His plants were covered 

 with ants of a different species from those that lived on the wild tree. 

 These ants frequented neither the foliary nectaries nor the spines, 

 which they neglected to perforate. Deprived of their usual inhabitants, 

 the spines differed from those of the usual plant, being but little devel- 

 oped, soft, and filled with a pulpy, sweetish substance. From this 

 experiment it may be concluded that the presence of ants within the 

 spines teuds to increase the size and density of those organs, which 

 can not reach their full development without the stimulus caused by 

 such inhabitants. 



It is to be supposed that the ancestors of the Acacia comigera had no 

 other defense against the attacks of herbivora than the protection 

 afforded by their spines. The differentiation of foliary nectaries at 

 first permitted them to utilize for their defense the constant visits dur- 

 ing the day of certain bees whose venomous stings would put to flight 

 the diurnal herbivora. But as the visits of these bees were only 

 diurnal, the plant would remain exposed to the attacks of nocturnal 

 herbivora. The adaptation of its spines for lodging the ants assured 

 the Acacia comigera of a constant defense. It id ay, however, be well 

 to remark that the defensive arrangements are especially directed 

 against leaf cutting ants rather than against other herbivorous crea- 

 tures. The protection given to ants is so necessary to this Acacia that, 

 according to Belt, its acclimation would be impossible in localities 

 where the Pseudomyrma does not exist. The leaves of the plant, even 

 when freed from the ants that inhabit them, are rejected by herbivorous 

 animals, their repugnance to them being due, in great part, to the odor 

 of ants exhaled by the leaves after they have been visited by the 

 Pseudomyrma. 



Beccari has mentioned a nutmeg tree (Myristica myrmecopMla) whose 

 internodes, provided with wing-like prolongations of very curious 

 form, are enlarged, hollow, and inhabited by ants, which reach the cav- 

 ities by openings situated on the stem or on the peduncle of the male 

 and female flowers. These openings have the form of narrow slits with 

 raised edges. The cavities of the various internodes do not intercom- 

 municate. We may suppose, by analogy with what is seen in other 

 myrmecophilous types, that the perforations do not exist in the young 

 internodes, and are the work of the ants that visit the plant in great 

 numbers, as they likewise do other species of the same genus. The 

 raised edges of the slits in the internodes apparently secrete a sugary 

 liquid attractive to ants. These insects, besides the part they may 

 play in driving off phytophagous creatures, may, perhaps, assist in the 

 fertilization of the dioecious flowers of the nutmeg tree. The visit of 

 insects is, in fact, indispensable to the fertilization of this plant, the 

 male flowers having a convex receptacle and an ovoid calyx slightly 

 tridentate at its upper part, and an andrcecium consisting of sixteen 

 anthers, forming a cylindrical stipitate column entirely included within 

 the tube of the calyx. 



