(72 SUMMARY OF CURRENT RESEARCHES RELATING TO 



7. General. 



Relationship between Ants and Plants in the Tropics.* — Herr 

 A. F. W. Scbiuiper publishes the results of ob.servations on the nature 

 of the comicction between myrmccophilous plants and the ants which 

 inhabit them in troincal America. 



The leaf-cutting ants are probably the most powerful enemy to which 

 vegetation is subject ia tropical and subtrojucal America. Other species 

 of ants, on the other hand, afford protection to vegetation by destroying 

 or keeping aloof the leaf-cutting ants and other enemies of plants. The 

 orange trees in the ]irovince of Canton in China are in this way protected 

 by nests of tree-dwelling ants. 



With regard to myrniecophilous trees and shrubs, the author states 

 that in most cases no special adaptation in the structure of the plant to 

 its habitation by ants can be proved. In other cases, however, observed 

 by him in Brazil, it is eviilent that such adaptations do exist, and this 

 is especially the case with Cecropia adenopus. In this and in otlier 

 species of the genus, the ants inhabit hollow cavities in the tubular intor- 

 nodcs, which serve, in the first place, to add to the flexibility of the 

 branches, but also as a dwelliug-ijlace for countless myriads of ants. 

 The protective function of these ants is shown by the facts that in every 

 specimen in which these cavities were not inhabited by ants, the leaves 

 were found to be entirely destroyed by leaf-cutting ants. In another 

 species of Cecropia which is not inhabited by ants, and which does not 

 possess these cavities, the tree is protected from the visits of the leaf- 

 cutting ants by the extreme smoothness of the stem, which is covered by 

 a coating of wax. In C. adenopus a special source of nutriment is fur- 

 nished to the ants which inhabit it, in a quantity of ovoid or pear-shaped 

 bodies, which cover the under side of the base of the leaf-stalk with a 

 velvety coating. These bodies, known as " Miillcr's corpuscles," are 

 probably mctamori)hoscd organs for the excretion of mucilage or resin. 

 They are but slightly attached to the hairs, and are very rich in albumi- 

 noid substances and in fatty oils. They are entirely wanting in the 

 species of Cecropia which are not inhabited by ants. In Acacia spjliaero- 

 cephala, the spines of which are inhabited by ants, similar bodies, which 

 serve for their nourishment, are found at the apex of the pinnae. If these 

 bodies are removed they are formed again with great rapidity. 



Extra-floral nectaries are regarded by Schimper, along with Belt and 

 Dclpiuo, as having for their primary function the attraction of friendly 

 ants which protect the plant from the attacks of leaf-cutting species. 

 The formation of the nectar in these nectaries may extend over a period 

 of several weeks. The nectaries are not in themselves directly service- 

 able to the plant, as can be shown by removing them, when the health 

 and vigour of the plant are not injured. The sugar in the nectar is 

 undoubtedly a product of the assimilating power of the leaf itself. 

 Extra-floral nectaries are especially numerous in the Tropics where the 

 leaf-cutting ants most abound ; and they are found most frequently in 

 the floral region, where they are most serviceable in rendering protection 

 to the organs of reproduction. 



• 'Die Wecbselbeziehungen zw. Pflanzen u. Ameiscu im tropischen Amerika,' 

 96 pp. and 3 pis., Jena, 1888. See Naturforscher, xxi. (1888) pp. 171-4. Cf. this 

 Journal, u.ntc, p. 87. 



