CHAP. XXVI COMMENSALISxM. PLANT-COMMUNITIES 95 



the distinctions. The plant-community is the lowest form ; it is merely a 

 congregation of units among which there is no co-operation for the com- 

 mon weal but rather a ceaseless struggle of all against all. Only in a 

 loose sense can we speak of certain individuals protecting others, as for 

 example, when the outermost and most exposed individuals of scrub 

 serve to shelter from the wind others, which consequently become taller 

 and finer ^ ; for they do not afford protection from any special motive, 

 such as is met with in some animal communities, nor are they in any 

 way specially adapted to act as guardians against a common foe. In 

 the plant-community egoism reigns supreme. The plant-community has 

 no higher units or personages in the sense employed in connexion with 

 human communities, which have their own organizations and their 

 members co-operating, as prescribed by law, for the common good. In 

 plant-communities there is, it is true, often (or always) a certain natural 

 dependence or reciprocal influence of many species upon one another ; they 

 give rise to definite organized units of a higher order ^ ; but there is no 

 thorough or organized division of labour such as is met with in 

 human and animal communities, where certain individuals or groups 

 of individuals work as organs, in the wide sense of the term, for the benefit 

 of the whole community. 



Woodhead ^ has suggested the term complementary association to 

 denote a community of species that live together in harmony, because 

 their rhizomes occupy different depths in the soil ; for example, he 

 described an ' association ' in which Holcus mollis is the ' surface plant ', 

 Pteris aquilina has deeper-seated rhizomes, and Scilla festalis buries its 

 bulbs at the greatest depth. The photophilous parts of these plants 

 are ' seasonably complementary '. The opposite extreme is provided 

 by competitive associations, composed of species that are battling with 

 each other. 



The classification and nomenclature of plant-communities are fully 

 discussed in Chapter XXXV. 



* See Chapter VIII, p. 2,7. ^ See, for instance, Grevillius, 1894. 



^ Woodhead, 1906, p. 345. 



