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ANIMAL LIFE IN THE TROPICAL FORESTS 
285 
veritable ants’ nests. When very young the stems are like 
small, irregular, prickly tubers, in the hollows of which ants 
establish themselves ; and these in time grow into irregular 
masses the size of large gourds, completely honeycombed with 
the cells of ants . 1 In America there are some analogous cases 
occurring in several families of plants, one of the most 
remarkable being that of certain Melastomas which have a 
kind of pouch formed by an enlargement of the petiole of 
the leaf, and which is inhabited by a colony of small ants. 
The hollow stems of the Ceeropias (curious trees with pale 
bark and large palmate leaves which are white beneath) are 
always tenanted by ants, which make small entrance holes 
through the bark • but here there seems no special adaptation 
to the wants of the insect. In a species of Acacia observed 
by Mr. Belt, the thorns are immensely large and hollow, and 
are always tenanted by ants. When young these thorns are 
soft and full of a sweetish pulpy substance, so that when the 
ants first take possession they find a store of food in their 
house. Afterwards they find a special provision of honey- 
glands on the leaf -stalks, and also small yellow fruit- like 
bodies which are eaten by the ants ; and this supply of food 
permanently attaches them to the plant. Mr. Belt believes, 
after much careful observation, that these ants protect the 
plant they live on from leaf-eating insects, especially from the 
destructive Saiiba ants, — that they are in fact a standing 
army kept for the protection of the plant! This view is 
supported by the fact that other plants — Passion-flowers for 
example — have honey-secreting glands on the young leaves 
and on the sepals of the flower-buds which constantly attract 
a small black ant. If this view is correct, we see that the 
need of escaping from the destructive attacks of the leaf- 
cutting ants has led to strange modifications in many plants. 
Those in which the foliage was especially attractive to these 
enemies were soon weeded out unless variations occurred which 
tended to preserve them. Hence the curious phenomenon of 
insects specially attracted to certain plants to protect them 
from other insects ; and the existence of the destructive leaf- 
1 These form two genera, Myrmecodia and Hydnophytum. For descrip- 
tion and figures see Mr, H. 0. Forbes’ Naturalist's Wanderings in the Eastern 
Archipelago, p. 79. 
