8 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 adapted themselves to those conditions. 

 The four groups just considered may 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. 



CHAPTER XXIII. 



ADAPTATIONS TO OTHER PLANTS AS SUPPORTS. 



Certain plants serve others as carriers, acting purely as 

 mechanical supports. To these supports plants have adapted 

 themselves in various ways. In many instances dead objects 

 of similar form may serve the same purpose. 'Hie supported 

 plants are, therefore, partly independent of the others, though 

 in most instances in nature they rely upon living supports. 



450. i. Climbing plants. — Climbing plants are those 

 which develop lateral organs, sensitive to contact, which be- 

 come recurved or coil about a support of suitable form and 



33" 



