134 PLANT LIFE 



which saturates the soil of peaty moorlands, 

 is not available for the vast majority of 

 plants, and they are consequently precluded 

 from occupying regions where such conditions 

 prevail. Those plants which do tolerate or 

 even demand them, often take in relatively 

 small quantities of the water, and they have 

 in consequence to limit the amount lost as 

 vapour in transpiration. In connection with 

 this limitation a variety of subsidiary modifi- 

 cations of habit may become manifest. Slow- 

 ness of growth, succulence, or the opposite 

 character of spininess, are common features; 

 whilst an evergreen habit with leathery leaves 

 is of fairly frequent occurrence amongst the 

 perennial plants of such localities. Indeed, 

 experience shows that any circumstance tend- 

 ing to reduce the amount of available water, 

 whether due to physical or physiological 

 conditions, will stamp its impress on the 

 vegetation. 



The onset of a period of drought will 

 speedily result in the extinction of entire 

 species within the affected area, and their 

 places will rapidly be taken by others which 

 are already adapted to these new conditions. 

 Which of the many possible forms of adapted- 

 ness to drought a particular colonist may 

 possess, depends of course on its own inherent 

 and hereditary properties. The part played 

 by the environment in the matter is merely 

 to rule out all those plants which are not 

 previously fitted in one way or another to 



