468 Ridley. Symbiosis of Ants and Plants. 
among and around the roots of the orchids and other such plants, unless the 
emission of the roots from the base of the stems in Dendrobiums in such 
a form that it is convenient for the ants can be said to be one. But, 
especially from observing young plants, I am of opinion that the nesting of 
the ants among the roots is distinctly advantageous, seedlings not infested 
by ants being weaker and suffering more from drought. In the case of the 
two epiphytic ferns, Platycerium biforme and Thamnopteris nidus-avis, ants 
also play a very important part in bringing soil to the roots in the nests of 
these nest-epiphytes. 
Thamnopteris. 
The Bird’s-nest Fern, Thamnopteris nidus-avis , L., is very abundant here, 
and appears as an epiphyte in all kinds of trees, frequently only a foot or two 
from the ground. Its large nest-like circles of fronds allow of its receiving 
and retaining fallen leaves, fruits, and other vegetable debris from the tree 
on which it grows, and through this mass the fronds are pushed up. The 
roots, dark brown and woolly, push up also through the decomposing leaves, 
and are especially prominent pushing through the dead fronds at the base of 
the plant. The decaying leaves and humus retained by the dead fronds not 
only feed the roots, but keep cool and moist the young growing fronds and 
roots, so that even on hot days when other epiphytes are suffering, this 
plant is little the worse. In the mass of dead leaves we find ants nesting. 
In one plant was a colony of the fierce, mahogany brown ant— Odonto- 
machuspunctulatus , Fab., apparently—which is so abundant in our forests ; 
known to many from its vicious stinging powers, its long usually wildly 
expanded jaws, and the extraordinary leaps that it gives when annoyed. It 
is one of the ants known as fire-ants here. Its sting is quite painful, and 
the effect lasts for some time. 
In another Bird’s-nest Fern was the nest of a species of Phidole which at 
first sight resembled Dolichoderus taprobane , but did not bite or sting. I am 
unable to identify the species, which was coloured much as in the Dolicho¬ 
derus t but was a more slender and hairy ant. 
These ants, there is little doubt, bring a certain amount of soil from 
the ground to form their nests among the fronds, and to a certain extent 
benefit the plant in this way, though this class of plants seems to depend 
more upon leaves accidentally blown or drifted in from trees near by. The 
amount of vegetable debris—leaves, fruits, and bits of stick and bark—which 
accumulates in the crown of this fern is surprisingly large. The fronds 
spread widely, however, and the circle of fronds has a diameter of from 6 to 
over 13 feet in large-sized plants; any leaf drifting within this circle is 
almost certain to slide to the centre. 
