OcroBeEr, Ig12.] THE ORCHID REVIEW. 299 
EPIPHYTES AND ANTS. 
AN article entitled ‘‘ Symbiosis of Ants and Plants,” by Mr. H. N. Ridley, 
F.R.S., Director of the Singapore Botanic Gardens, recently appeared in 
the Annals of Botany, and under the heading “ Relations of Ants to 
Epiphytes,”’ we find-some interesting remarks on the conditions under which 
certain epiphytic Orchids grow in the tropics. 
Ants, Mr. Ridley remarks, play a considerable part in many cases in the 
growth of epiphytes, and especially in Orchids. All trees do not bear 
epiphytes. On some of those with smooth bark or with longitudinally 
grooved bark epiphytes are seldom if ever to be found. Whether a tree 
does or does not bear epiphytes depends on the flow of rain down the 
branches and stem. Where in smooth-barked trees like Macaranga the 
rain flows quickly off, vegetable debris and spores cannot rest, and no 
epiphytes are borne. A notch in the bark of one of these may, however, 
retain a little soil, and epiphytes then usually appear. Lichens are 
abundant on these smooth-barked trees, and usually absent from rough- 
barked ones. Ficus Benjamina is a smooth-barked tree, but liable to cracks 
or other injuries, so that it carries epiphytes readily in parts. The boughs 
are covered with lichens, and where they are more or less vertical, with a 
strong slope, nothing more grows on the upper side where the great rush of 
rain-water takes place. On the sides where water more slowly trickles off, 
mosses and Algz starting from a crack in the bark commence growing. 
As they increase in growth they retain more and more of the debris, and 
may cover a considerable patch. In doing so they kill out the lichens. 
When the patch is large enough, ferns or phanerogamous plants appear. 
The roots of the Orchids and creeping rhizomes of the ferns retain the 
vegetable debris washed down and blown by the wind, and the plants 
increase until the bough may be covered with epiphytes. 
As soon as the Orchids commence to grow, or even before, the ants 
begin to use the spot as a suitable one for their nests. The Pigeon-Orchid 
(Dendrobium crumenatum) is one very attractive to ants. It emits slender 
white roots so as to form a cage at the stem base, which is quickly occupied 
by a species of ant, a Dolichoderus. This ant brings a quantity of soil and 
piles it up, and fills in the spaces between the roots beneath which it 
makes the nest. The earth thus brought up supplies food to the plant and 
also serves to keep the roots ccol and moist. The old nests, as time goes 
on, accumulate on the tree boughs till quite a quantity of soil is supplied to 
the roots of the various epiphytes. 
I do not find that all the great number of epiphytic plants on our trees 
are supplied in this way with nutriment, but undoubtedly it is one of the 
factors of the great development of epiphytes in the Eastern Tropics. 
