SYMBIOTIC PLANTS 291 



instances of vegetable partnership and messmatism, in 

 which, two different plants live together to their mutual 

 advantage, particularly in relation to nutrition. Lichens 

 are remarkable examples of this partnership, but as we 

 have already considered them to some extent (p. 112) 

 there is no need to describe them in this place. We 

 have also referred to the Bacteria in the root-nodules 

 of leguminous plants (p. 13) — another instance of sym- 

 biosis. Perhaps even more remarkable than these plant 

 partnerships are those which have been noted between 

 plants and animals. There is the case of the rotifer and 

 the Liverwort, Frullania dilatata{p .131). Minute green 

 Algae thrive in the body of the fresh- water Hydra viridis. 

 Certain moths lay eggs in the carpels of Yucca, and the 

 larvae which emerge from the eggs feed on the seeds of 

 the plant; but the seeds would not mature, and conse- 

 quently the larvae would perish did not the moths carry 

 pollen from anthers and Hterally force it into orifices in 

 the stigmas. The moths thus enable the Yiicca to ripen 

 fruit, and the plant in return for the service does not 

 grudge the larvae a modicum of seed as food. The 

 naturalist Belt was the first to call attention to the 

 BuU's-horn Acacia {Acacia cornigera). The stipules of 

 this plant have been modified into hollow thorns, in 

 which certain warrior ants reside. The tree provides 

 the ants with food, and the ants in return defend the 

 tree against the incursions of leaf-cutting ants, which 

 threaten dire damage. This association between plants 

 and ants is called " myrmecophUy," from the Greek 

 myrmex, ant. 



Saprophytes, numerous among the Bacteria and 

 Fungi (see pp. 13 and 99), derive their carbohydrates, 



