THE WEB OF LIFE 287 



are tenanted by ants (Iridomyrmex myrmecodius). Beccari 

 thought that the ants were responsible for making the laby- 

 rinth, but Forbes and Treub proved that there could be 

 typical labyrinths in the entire absence of ants. It seems 

 certain, indeed, that the tuber is a water-absorbing and 

 water-storing organ, very useful to a plant which Uves quite 

 off the ground. At the same time the association with ants 

 is very general. Miehe points out that some of the walls of 

 the maze are smooth and light brown, while others are 

 warty and dark brown. A dark fungus grows on the rough 

 surfaces, not on the smooth. The ants deposit their 

 excrement on the rough surfaces ; they use the smooth- 

 walled chambers as nurseries. It is probable, Miehe thinks, 

 that the excrement of the ants is utihzed by the plants ; 

 and this, if the case, may be a very useful arrangement for 

 an epiphyte living off the groimd. The ants get a conveni- 

 ent shelter. They do not seem to eat anything that be- 

 longs to the plant, though what they eat is unknown. 

 Nor do we know whether they can get along without their 

 maze. 



Epizoic Associations. — Many plants, such as Lichens 

 and Orchids, grow upon other plants, and are known as 

 epiphytic, and the term may be also appUed to animals 

 which are practically confined to certain plants, e.g. various 

 Hydrozoa and Polyzoa on seaweeds, not in any real para- 

 sitism, but because the situation suits them well. Similarly, 

 we have epizoic plants and animals. The green Alga on 

 the Sloth's hair is epizoic. The seaweed on the limpet's 

 back is epizoic. We do not know that there is any value 

 in the last association, though with some slight change of 

 conditions it might readily become invested with such 

 value. In the same way there are many examples of 



