SOME kkmarkablp: adaptations of plants to insects. 97 



ON SOME REMARKABLE ADAPTATIONS OF PLANTS TO 



INSECTS. 



By Rev. Prof. G. Henslow, M.A., Y.M.H. 



Xectuie given on June 26, 1906.] 



As adaptations to external conditions of all sorts occur in all parts of 

 plants, I propose selecting a few examples of special cases in connection 

 with insects and hamming birds, taking as examples ant-domatia and the 

 cultivation of fungi by ants, the pollination of Salvia and Coryanthes by 

 bees, Marcgravia by birds, and the ovary-gall of the "wild" fig, or 

 Caprificus, 



Ant-domatia. 



The first person to notice and describe the stipular domatia of a 

 species of ant {Fseudomyrma hicolor, Guer.) in the "buli's-horn thorn" 

 acacia (A. sphczroceijhala) was T. Belt. He thus wrote : — * 



" This acacia has bipinnate leaves and grows to a height of 15 or 20 

 feet. The curved horn-like stipules are hollow and tenanted by ants, 

 which make a small hole for their entrance and exit near the pointed end. 

 They also burrow through the partition that separates the two horns. 

 Here they rear their young, and in the wet season every one of the thorns 

 is tenanted ; while hundreds of ants are to be seen running about, especially 

 over the young leaves. If one of these be touched, or a branch shaken, 

 they swarm out from the hollow thorns and attack the aggressor with 

 jaws and sting. They sting severely, raising a little white lump that does 

 not disappear in less than twenty-four hours. 



" These ants form a most efficient standing army for the plant, which 

 not only prevents the mammalia from browsing on the leaves, but delivers 

 it from the attacks of a much more dangerous enemy — the leaf-cutting 

 ants. For these services the ants are not only securely housed by the 

 plant, but are provided with a bountiful supply of food ; and to secure 

 their attendance at the right time and place this food is so arranged and 

 distributed as to effect that object with wonderful perfection. At the base 

 of each pair of leaflets, on the midrib, is a crater-formed gland which 

 when the leaves are young secretes a honey-like liquid. Of this the ants 

 are very fond ; and they are constantly running about from one gland to 

 another to sip of the honey as it is secreted. But this is not all ; there is 

 a still more wonderful provision of more solid food. At the end of each 

 of the small divisions of the compound leaf there is, when the leaf first 

 unfolds, a little yellow fruit- like body united by a point at its base to the 

 end of the plumule. It resembles a golden pear. When the leaf first 

 unfolds these little ' pears ' are not quite ripe, and the ants are continually 

 employed going from one to another examining them. When an ant 

 finds one sufficiently advanced it bites the small point of attachment ; 

 then bending down the fruit-like body, it breaks it off and bears it away 

 * Tlie Naturalist in Nicaragua, p. 218 (1874). 



H 



