214 Yapp. — Two Malayan ‘ Myrmecophilous ’ Ferns. 
away behind the walls of the deep sorus-cups 1 ; while above, 
the tightly packed sporangia, protected by their strongly 
thickened annuli, would probably suffer little, even in the 
heaviest downpour. 
The question as to the function to be ascribed to the 
galleries in these Ferns is more complicated. Three possi- 
bilities present themselves. First, that the galleries are a 
special adaptation on behalf of the ants, both the plant and 
its guests deriving benefit from the symbiosis. The second 
is that they are more or less accidental, simply replacing the 
effete aqueous tissue of the stem, and themselves serving no 
special purpose ; while a third possible explanation is that 
they may be connected with the interchange of gases in the 
stem, as suggested by Treub 2 in the case of the ant-galleries 
of Myrmecodia. 
Nothing approaching the extensive and regular system of 
hollows traversing the stem in these Ferns appears to be 
known among the other Filices, though a few closely allied 
Malayan species 3 , which are also inhabited by ants, in all 
probability possess similar structures. At the same time, 
cavities in the stems of other Ferns are by no means unknown. 
For instance, Ceratopteris thalictroides , Brong., possesses 
hollow spaces of schizogenous origin in the cortical tissues 
of both stem and root. Campbell 4 states that — 
‘ In Onoclea struthiopteris characteristic air-chambers are 
formed in the young medulla at an early period. At certain 
points the cells become longer and their contents more 
transparent. These cells divide less rapidly than the sur- 
rounding tissue, and large intercellular spaces are formed. 
The loose cells about these form masses of trichomes, either 
1 Christ (’96), p. 93, points out that many of the species of Polypodium found in 
the rainy mountainous districts of the Malay Archipelago possess these deeply 
sunken sori. He regards them as a protection against heavy rains, such an adapta- 
tion being especially necessary in this genus, as the indusium found in most other 
Ferns is absent. 
2 Treub (’88), p. 206. 
3 Such are Polypodium lomarioides, Kze., P. sarcopus , De Vriese et Teysrn., and 
the remaining species of Blume’s genus Lecanopteris. 
4 Campbell (’95), p. 323. 
