MESSMATES, MUTUALISTS, AND PARASITES 



75 



epi, upon; phyton, a plant). The advantage to the Orchids is 

 obvious, though they do not absorb the sap of the plants upon 

 which they live. These last, however, apparently derive no 

 benefit from this one-sided arrangement. 



There are numerous cases of commen- 

 salism between plants and animals in which 

 the latter alone are benefited. In one of the 

 Liverworts (Frullania dilatata, fig. 1069) 

 which grow on tree-trunks there are little 

 cup -like outgrowths on the under sides of 

 the leaves, serving as the abodes of a species 

 of Wheel- Animalcule (Callidina symbiotica]. 

 Marine plants often bear animals as mess- 

 mates, which do them no harm. On a kind 

 of brown sea-weed (Fucus serratus}, for ex- 

 ample, are frequently to be seen the little 

 spiral tubes of a sort of Annelid (Spirorbis], 

 which no doubt secures an increased supply 

 of nutriment and dissolved oxygen by being 

 moved about in the water when the tide is 

 up. The Australian Sea -Horse (Phyllop- 

 teryx eques) also benefits by its association 

 with the sea -weeds to which it bears a 

 resemblance (see vol. ii, p. 296). 



Some instances are known of commen- 

 salism between a plant and an animal, in 

 which both derive advantage from the as- 

 sociation. Ant -plants illustrate such an 

 arrangement (see p. 81), and so do the 

 Sloths of South America, in which minute 

 algae live in the grooves of the fluted p2^fe%2?S 

 hairs. For these algae are provided with in which a Rotifer */** *- 

 a sheltered home, and at the same time 

 give a greenish tint to the hairs, the 

 Sloths being thereby rendered less conspicuous to their enemies. 



MUTUALISM (Symbiosis). Organisms living together as Mutu- 

 alists are very intimately associated for mutual benefit. Mutualism 

 between two plants is well illustrated by leguminous forms and 

 the minute fungi which live in the tubercles on their roots. And 

 every Lichen may be regarded as a joint-stock community, con- 



biotica) lives : enlarged. The small 

 drawing is of one cup with its Rotifer 

 (further enlarged). 



