7 6 



PLANTS 



apply to all plants in all circumstances under which they are 

 found to thrive, although the environment may be very different 

 from that which is normal to the plants we have been consider- 

 ing. In order, then, to test the validity of this law, let us ex- 

 amine the flora of localities which present conditions different 

 from those we have already considered, 



FIG. 36. A tree deformed by the action of the wind and salt spray. The 

 buds are continually killed on the windward side. Coast of North Carolina. 

 A similar effect is produced by the combined action of wind and cold, as on high 

 mountain summits. 



Water 



183. With regard to conditions of moisture, plants have been 

 grouped into three classes, mesophytes, hydrophytes and 

 xerophytes. Mesophytes are the plants which grow normally 

 under conditions of moderate supply of moisture, and hence 

 include all those which we have heretofore been studying. 

 Hydrophytes are plants which grow in the water, or, at least, 

 in very wet soils. Xerophytes are the plants peculiar to arid 

 regions. 



184. Among hydrophytes we may have, first, those plants 



