16 



BRITISH PLANTS 



woods, and of evergreen woods there are several types, 

 each characterized by a special kind of climate. Thus 

 we have the evergreen rain-forests of the Tropics, with 

 a climate exceedingly hot and moist ; the coniferous 

 evergreen forests of Northern Russia, where the climate 

 is cold Fnd dry ; and the evergreen dry- woods of Southern 

 Europe, where the climate is dry and warm. 



We seo from this that the physiogiiomic groups into 

 which we have divided the vegetation (woodland, grass- 

 land, healh, etc.) are only in part associated with 

 definite types of climate. A nearer approach to a 

 clin atic grouping is obtained if we spHt up the physiog- 

 nonic groups into subdivisions founded upon climatic 

 difl^srences, thus : 



In this country the only natural deserts we have are 

 sea-beaches and sand-dunes. The desert is an open type 

 of habitat, containing many bare spots where plants are 

 practically free from competition. Artificial open habi- 

 tats are produced in cultivated fields and waste places 

 frequently disturbed by man. When the ground is 

 fully occupied by plants, the habitat is said to be closed, 

 and where this has happened, a stable community of 

 plants or associations of plants is established. 



The number of physiognomic divisions into which 

 vegetation may be divided is, of course, a matter of 



