THE NEW FIELD-BOTANY 355 



must be able to identify these characteristic moorland 

 plants, so that he may make careful note of the various 

 species, and determine those which predominate, those 

 which are subdominant, those which occasionally occur, 

 and also those that are rare. Rarities and occasionals, 

 however, while interesting, have not the principal interest 

 to the ecologist; he is mainly concerned with the plants 

 which give a distinct floristic physiognomy to the habi- 

 tat. To a student who has an " eye " for landscape, 

 and is able to identify plants, this first stage in ecological 

 inquiry is not difficult. 



Having noted the various species that form distinct 

 communities, the ecologist proceeds to make further 

 inquiry. He has to ascertain why a particular species 

 has a peculiar habit and is found in a given environ- 

 ment, why various species are associated in com- 

 munities, why those communities have a characteristic 

 appearance, and, moreover, he must try to understand 

 the economy of the plants concerned, the nature of the 

 demands they make upon their environment, and the 

 manner in which they are adapted thereto. This is a 

 big inquiry, but a worthy and interesting one. It must 

 be remembered that a plant which thrives in a given 

 environment is both internally and externally in harmony 

 with it. If the natural conditions change and the species 

 cannot meet the demands of the change, it will go under 

 in the struggle for existence, and its place will be occupied 

 by other species better adapted to the changed con- 

 ditions. 



In studying plants in relation to their environments, 

 the student has to take into account a number of eco- 

 logical factors, such as light intensity, temperature, 



