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in ANIMAL LIFE IN THE TROPICAL FORESTS 285veritable ants' nests. When very young the stems are likesmall, irregular, prickly tubers, in the hollows of which antsestablish themselves ;and these in time grow into irregularmasses the size of large gourds, completely honeycombed withthe cells of ants. 1 In America there are some analogous casesoccurring in several families of plants, one of the mostremarkable being that of certain Melastomas which have akind of pouch formed by an enlargement of the petiole ofthe leaf, and which is inhabited by a colony of small ants.The hollow stems of the Cecropias (curious trees with palebark and large palmate leaves which are white beneath) arealways tenanted by ants, which make small entrance holesthrough the bark but here there seems no;special adaptationto the wants of the insect. In a speciesof Acacia observedby Mr. Belt, the thorns are immensely large and hollow, andare always tenanted by ants. When young these thorns aresoft and full of a sweetish pulpy substance, so that when theants first take possession they find a store of food in theirhouse. Afterwards they find a special provision of honeyglandson the leaf -stalks, and also small yellow fruit- likebodies which are eaten by the ants and this ; supply of foodpermanently attaches them to the plant. Mr. Belt believes,after much careful observation, that these ants protect theplant they live on from leaf-eating insects, especially from thedestructive Saiiba ants, that they are in fact a standingarmy kept for the protection of the !plant This view issupported by the fact that other plantsPassion-flowers forexample have honey-secreting glands on the young leavesand on the sepals of the flower-buds which constantly attracta small black ant. If this view is correct, we see that theneed of escaping from the destructive attacks of the leafcuttingants has led to strange modifications in many plants.Those in which the foliage was especiallyattractive to theseenemies were soon weeded out unless variations occurred whichtended to preserve them. Hence the curious phenomenon ofinsects specially attracted to certain plants to protect themfrom other insects ;and the existence of the destructive leaf-1These form two genera, Myrmecodia and Hydnophytum. For descriptionand figures see Mr. H. 0. Forbes' Naturalist's Wanderings in the EasternArchipelago, p. 79.