CHAPTER XXII 



PLANT ASSOCIATIONS AND FORMATIONS 



In tlie course of tljis book we have made several attempts 

 to classify plants ecologically. The simplest and most 

 obvious was to divide the vegetation into types according 

 to their appearance when beheld as masses of individuals 

 in the landscape. This physiognomic grouping gave us 

 the great types of vegetation which we know as wood- 

 land, moorland, grassland, and desert (p. 16). We 

 found that these types could only be associated with a 

 definite kind of cHmate if subdivided according to climatic 

 differences. This led us to a climatic grouping of plants 

 (p. 16). Later on, in dealing with the relation between 

 water and plants (Chapters II. to VI.), and then with the 

 relation between water and the soil (Chapter IX.), and, 

 last of all, between the soil and the plant (Chapter X.), we 

 were forced to enlarge our conceptions of climate. Most 

 of the climatic factors act indirectly upon the plant 

 through the soil, and when we come to consider the details 

 of the vegetation, the soil as the exponent of climate 

 becomes more and more important (p. 84). 



We pointed out on p. 17 that a satisfactory and 

 scientific ecological grouping of the vegetation can only 

 be obtained if we take into consideration all the external 

 factors of the environment influencing the vegetation. 

 Some factors, of course, are more important than others, 

 but almost any factor may, in some place or another, 

 assume an importance which will leave a stamp on the 

 vegetation growing there. Considered thus, the term 

 habitat has a special meaning when used in ecology. If 

 means the abode of a plant or community of plants as 

 biologically conditioned by the factors of the environment. 

 In defining the habitat of any plant, therefore, we must 



223 



