Symbiosis of Ants and Plants. 
BY 
H. N. RIDLEY, M.A., F.R.S., F.L.S. 
Director of the Botanic Gardens, Singapore. 
With Plates XXXV and XXXVI. 
A GREAT deal has been written and published in various works concern¬ 
ing the adaptations of certain plants in the tropics apparently for 
the combined benefit of ants and the plants themselves, each deriving some 
advantage from the symbiosis. The subject, however, has by no means 
been exhausted, as in many cases the observations made by the writers 
have been too few, or derived from too short an acquaintance with the 
plants in their natural habitat. The most important general contribution, 
at least to the study of the myrmecophilous plants of the Eastern Tropics, 
has been made by O. Beccari, in Malesia (‘ Piante ospitatrici ’), but the story 
of some of the species he has described in this paper is still incomplete, and 
more remains to be done. Myrmecophilous plants, using the word in its 
widest extent, are, it would seem, commoner in the Eastern Tropics than 
in those of the New World, and we possess in the Malay Peninsula a con¬ 
siderable number of plants which have, or are believed to have, close 
relations with ants, many of which plants occur wild or introduced in the 
Botanic Gardens in Singapore. These are the following :— 
Pachycentria, 
Myrmecodia, 
Hydnophy tu m , 
Clerodendron myr mecoph ilu m , 
Dischidia Rafflesiana , 
Ficus inaequalis , 
Macaranga , 3 species, 
Kortkalsia , 2 species, 
Pleopeltis sinuosa , 
Lecanopteris car nos a, 
besides a number of epiphytes in the life-history of which ants play a more 
or less important part. Among these and so-called myrmecophilous plants 
generally there are many degrees of symbiosis. In some species, and these 
are not many, we have distinct modifications, which cannot apparently 
be of any use at all except to induce ants to take up their abode in or about 
the plant, and in which observation shows that the absence of the ants pro- 
[Annals of Botany, Vol. XXIV. No. CXIV. April, 1910.] 
