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. 
BroLocicAL CLASSIFICATION OF PLANTS IN RELATION TO WATER. 
Water-plants (Chapter V.) Land or Terrestrial plants. 
(Aquatics, Hydrophytes). 
1 
\ 
Plants showing constant characters Tropophytes (Chapter VI.) 
all the year round (Chapter III.). 
] 
| | eh | | | 
Hygrophytes Mesophytes Xerophytes Hygrophilous Mesophilous Xerophilous 
Tropophytes Tropophytes Tropophytes 
