74 



ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



these traps is by no means clear, but minute crustaceans, &c. r 

 are fond of prying into holes and corners in search of food, while 

 some of them may make use of the two branching bristles as a 

 place of refuge from their enemies. And as the two bristles act 

 as guides to the mouth of the trap the result is often tragic. 

 Slimy hairs grow in this dangerous neighbourhood, which pos- 

 sibly have attractions to offer, while the little transparent door 



Fig. 1068. Traps of Bladderwort (Utricularia], enlarged, i , External view. 2, Longitudinal section. 

 3, Three absorptive branched hairs from interior, i and 2, X 4; 3, X 250. 



must look like a spot of light, and perhaps acts as a lure. It is 

 at any rate certain that victims are numerous, and their decom- 

 posed remains are absorbed by curious branched hairs which 

 line the trap. The prey is apparently not digested as in Sundews 

 and Butterworts. 



The remaining topics dealt with in this chapter also more or 

 less involve questions of nutrition, but are placed under separate 

 headings for the sake of clearness. 



ASSOCIATION OF PLANTS AND ANIMALS AS MESSMATES, 

 MUTUALISTS, AND PARASITES 



COMMENSALISM. Two associated organisms are known as 

 Messmates or Commensals when they live together to the benefit 

 of one or both; the union, however, not being of so intimate a 

 nature as to be essential to the life of either. The term commen- 

 salism was coined to express such relations as existing between 

 different animals, but there appears to be no reason why its mean- 

 ing should not be extended to cover cases where two plants, or a 

 plant and an animal, are similarly related. As an instance of the 

 former we may take those tropical Orchids which regularly live 

 upon trees, and are on that account said to be Epiphytes (Gk. 



