THE FERX BULLETIN 



109 



cumulation of an aerial "soil" in the mossy forest and 

 in tree-top gardens at lesser altitudes ; epecial humus- 

 collecting structures such as have just been described ; 

 the insectivorous habit in Nepenthes and the attrac- 

 tion of insects for the debris they bring or for their ex- 

 creta or their carcasses as with the plants now under 

 discussion. The plants waste none of their parts for 

 the support of the ants, offering them only a tolerably 

 moist shelter and this is very evidently a sufficient in- 

 ducement for the ants to seek them for I have never 

 found a healthy individual of one of those plants with- 

 out its tenants. The latter are not specialized in adap- 

 tion to their specific hosts for the same ant inhabits the 

 chambers of different plants; for instance, I have 

 found one kind in Polypodium sinuosum, Myrtnecodia 

 and Hydnophyllum all in a single tree. 



Although ants have not the reputation of being un- 

 tidy house-keepers, the chambers which they occupy 

 are never entirely clean. The plant can of itself, effect 

 the quick removal of liquid ejecta; it can get rid of 

 solid ones only as they are dissolved. I have found a 

 fungus in an apparently healthy Polypodium sinuosum 

 growing in the lining of the chamber and at first I im- 

 agined it might be analogous in function to mycorhiza, 

 but it is not always present and it is probably merely 

 accidental. Both of these ferns are without roots 

 other than such as are necessary for their firm attach- 

 ment and they habituality grow on bare branches, 

 without any mass of epiphytes ; therefore they would 

 be in special straits for mineral food if it were not for 

 their tenants ants. Nevertheless they are conspicuous 

 for the ready falling of their leaves conclusive evi- 

 dence that they are not in practice obliged to husband 

 their ash constituents. The fact that Polypodium 



