CHAPTER X 

 PLANT ASSOCIATIONS 



ALTHOUGH the number of species of plants making up the flora, 

 even of such a small area as England, comprises several thou- 

 sands, yet every one knows how frequently large tracts of country 

 are mainly occupied by one species, which gives to the vegetation 

 its characteristic aspect. This is so true of natural woodland 

 that it is possible to speak, as we saw in the last chapter, of Oak, 

 or Pine, or Birch woods, as the case may be. Similarly, heaths 

 are practically taken possession of by one or two species of grasses, 

 and so too are our pastures and meadows, although, when more 

 closely examined, the vegetation is found to be more diverse than 

 a casual glance would lead us to suppose. 



THE SOCIAL HABIT 



Trees and Grasses are the best instances of the social habit in 

 plants, but they are by no means the only ones. Many Sea- 

 weeds, and also plants belonging to marshy ground, exhibit this 

 tendency, which as a rule is more marked in aquatic than in land 

 plants. The Sea-w r eed, Sargassum bacciferum, of the Sargasso Sea ; 

 the Grass, Phragmites communis ; and the Reed, Scirpus lacustris, 

 are some of the most familiar examples. Among land plants, 

 in addition to trees and grasses, may be mentioned Mosses and 

 Liverworts, and such flowering plants as Heather and the Willow- 

 Herb. The effect of agricultural operations, too, is to increase 

 the domain of certain social plants ; for many wild species are 

 destroyed, whilst a particular species is being cultivated for food. 



Certain plants, on the other hand, may be said to have the 

 social habit developed in a different way. They are found living 

 a life of close relationship, not with their own, but with other 

 species. Many Lichens and Fungi, certain Mosses and Liver- 



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