64 BRITISH PLANTS 



This does not matter in summer, when the soil is warm, 

 for there is plenty of water, and the roots are active. In 

 winter, however, the water is cold, and there is danger 

 of excessive transpiration. For this reason most marsh- 

 plants are tropophytes, and die down in winter. Those 

 that remain evergreen show xerophytic characters (p. 31). 

 When the water becomes sour, the marsh passes over 

 into the bog, and the number of xerophytic forms in- 

 creases. The same thing happens as it becomes salt, the 

 salt-marsh vegetation becoming markedly xerophytic. 



BIOLOGICAL CLASSIFICATION OF PLANTS IN RELATION TO WATER. 



Water-plants (Chapter V.) Land or Terrestrial plants. 



(Aquatics, Hydrophytes). 



Plants showing constant characters Tropophytes ^ Chapter VI.) 



all the year round (Chapter HI.). 



" philous Mesop'hilous Xeropl 



phytes Tropophytes Tropophytes 



Hygrophytes Mesophytes Xerophytes Hygrophilous Mesopnilous Xerophilous 



