S II. ADAPTATIONS TO OTHER PLANTS. 



449. Plant associations. — Each set of external conditions 

 brings about the association of certain plants "with each other, 

 because they have ada]ited themselves to those conditions. 

 The four groups just considered nia}' be looked upon as plant 

 societies of the most general kind. Within each of these 

 four it is possible to distinguish a number of smaller societies 

 determined by a more limited range of conditions. 



Besides these plant associations, however, there are those 

 which are determined by the relation of the plants to each 

 other, as affording mechanical support, or assistance in the 

 work of nutrition. The plant associations of this kind only 

 are now to be considered. 



CH.VPTKR XXIII. 



ADAPTATIONS TO OTHER PLANTS AS SUPPORTS. 



Certain plants ser\-e others as carriers, acting ])urely as 

 mechanical sujiports. To these supports plants have ada])ted 

 tlieuiseh'cs in -warious wa)-s. Tn man\- iiislances dead objects 

 of similar form may serve the same ])ur]-iose. The supjiorted 

 plants are, therefore, jiartly independent of Ihe others, though 

 in most instances in nature the)- rel\' upon living supports. 



450. I. Climbing plants. — Climbing plants are those 

 which develop Literal organs, scnsiti\e to contact, which be- 

 come recur\'ed or coil about a support of suitable form and 



