INTEODUCTION 



THE UNITS OF VEGETATIOX THEIS RELATIONSHIPS 



AND CLASSIFICATION 



It has been well said by the distinguished plant- 

 geographer Professor Drude of Dresden that plants may 

 be studied in pure science from three points of view, and 

 from three only: — the physiological, the phylogenetic 

 and the geographical. Geographical Botany or Plant- 

 geography may be defined as the study of the facts and 

 causes of the distribution of plant-life over the surface of 

 the earth. 



When we consider the distribution of the plant-life 

 of any given region or country, whether large or small, 

 we find that it may be regarded from two distinct points 

 of view. In the first place we may study the distribution 

 of the species, and, in the case of the larger areas of the 

 earth, the distribution of the genera and families of plants. 

 The Kst of species, arranged taxonomically, is called the 

 flora of the region or country, and the study of their 

 distribution is floristic plant-geography. 



But there is another way of regarding the distribution 

 of plant-life. If we consider the general plant-covering 

 or vegetation of any geographical region we find that 

 it is naturally divided into units, each of which has a 

 characteristic appearance or physiognomy and consists 

 of characteristic species. These vegetatiort^ 

 Vegetation- units have been recognised from the earliest 

 units orpiaJi^ times, since not only do they form outstanding 

 conun features of all landscapes, but man absolutely 



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