PLANT ASSOCIATIONS 127 



keenly for position, light, food and moisture. From this mode of 

 life it follows that species with similar requirements will tend to grow 

 together, and thus communities of species are formed, such as exists, 

 for example, on the sand dunes or moors, or in the woods, marshes, 

 or lakes. These plant communities or associations can be regarded 

 as parcelling out the whole country between them, each variety being 

 developed where the conditions of life are most suitable. In these 

 associations the species are not arranged anyhow. A definite order 

 can usually be distinguished, which is approximately constant where- 

 ever the particular association occurs. Examine a wood, for example, 

 in Britain, and it will be found that, as a rule, only one or two 

 species of tree predominate almost invariably beech, oak, Scots 

 pine, or birch. Competing with the dominant tree are others which 

 only await the opportunity, in the form of some change of conditions, 

 to supersede it and in their turn, predominate. With these, again, 

 are other trees, such as the ash, which are always more or less 

 solitary and secondary in an association. In the shade under the 

 trees a subordinate vegetation is developed which is quite char- 

 acteristic for each type of woodland, and which varies according to 

 the amount of light, humus, or moisture. This subordinate vegeta- 

 tion has likewise its dominant, secondary, and solitary species. Thus 

 each association presents a definite hierarchy of forms." 



" The method of study here suggested is, in practice, a survey by 

 means of a series of excursions, of the characteristic plant associa- 

 tions of the region. In Britain almost any district, however circum- 

 scribed, will give a wide range of vegetation, especially in those 

 parts where hills are near the sea." 



Eobert Smith also pointed out the bearing which this work has on 

 the teaching of school geography, which should rightly begin with 

 the study of the home district and apply " the knowledge acquired 



