466 Ridley.—Symbiosis of Ants and Plants. 
After the drought I was hardly able to find a single living plant anywhere. 
The rhizomes completely dried up and hundreds of plants must have 
perished. Meanwhile, Davallia solida , Polypodium angustifolium , and other 
such plants seemed to be little the worse, though as much or even more 
exposed. Vittaria lineata feels the effect of drought severely, and its thin 
wiry rhizomes seem to dry up very much, while the fronds get wilted and 
dry, but I do not think that even it perishes so readily as Polypodium 
sinuosum . As a water reservoir, therefore, the rhizome (at least in its 
present state, with the ant galleries replacing the original large-celled tissue) 
must be considered a failure. 
But whether the galleries are intended for the absorption of water 
or for aeration of the stem, the question arises, What benefit, if any, does 
the plant derive from the presence of ants in the galleries ? Their use as 
defenders against the attacks of caterpillars may, I think, be laid aside. 
I have never seen any of the epiphytic ferns attacked by caterpillars or any 
other injurious insects. In fact it is comparatively rare to find any ferns 
here attacked by insects at all. Angiopteris evecta injured by a caterpillar 
which rolls up the ends of its fronds into a ball, and Aspidium cicutarium 
attacked by a small species of bag-worm, are all the ferns that I can recall 
having seen damaged by insects. 
Lecanopteris carnosa , Bl., of which Yapp gives an account in the same 
paper in which he deals with Polypodium sinuosum , is another of our ant- 
inhabited plants apparently specially modified for their benefit. He is 
doubtless right in classing it as a Polypodium near P. sinuosum. It is 
usually met with in very damp forests at a considerable altitude, where 
it grows on wet mossy branches of trees, often at some height. Plants, 
however, occur also on more dry and exposed positions, as it still grows 
on the branches of lofty Shoreas on the top of Bukit-Timah, a hill of 
500 feet elevation, in Singapore. Here it is certainly in a comparatively 
dry exposed habitat, but from the occurrence in the same spot of other 
plants more usually found at a considerable altitude, I am inclined to think 
that this hill was originally of a much greater altitude than it is at present, 
and was then covered with high wet forest. 
The rhizome of this fern is rounded and of very considerable size. 
It is very fleshy and tunnelled with hollow spaces similar to those in 
Myrmecodia , and tenanted by ants described by Forel as Crematogaster 
Yappii. 
Relation of Ants to Epiphytes. 
Ants play a considerable part in many cases in the growth of epiphytes, 
and especially in orchids. 
While not intending here to go into the question of the epiphytic life 
of plants in the Eastern Tropics, I would, however, record some observa- 
