INFLUENCE OP WATER ON PLANT-LIFE 31 



3. Mesophytes. 



Some plants are pronounced hygrophytes, others pro- 

 nounced xerophj'tes. Hygrophytes lie, in their relation 

 to water, at one end of a series which is terminated at 

 the other extremity by the highly specialized xerophytes. 

 Between the two lie a vast host of plants, generally 

 known as mesophytes, which possess no marked char- 

 acters either way. Such plants live in conditions which 

 are fairly favourable to the plant aU the year round. 

 The true mesophyte is an evergreen, and lives only in 

 the Tropics or in regions not far removed from them. 

 Any winter-break would entail the assumption of some 

 more or less marked xerophytic characters. We have 

 no true mesophytes in Great Britain because the inter- 

 ruption of winter is too pronounced. The nearest plants 

 we have to them are certain niarsh - plants hke the 

 iris. If the winter is mUd, the leaves of the iris persist 

 to the spring. The leaves are long, band-shaped, and 

 erect. The latter is a xerophytic character (p. 46). Amid 

 a host of hygrophytic characters, the iris, therefore, has 

 at least one xerophytic character — it avoids the light 

 by turning its leaves edgewise to it. If, however, the 

 winter is severe, the leaves aU perish, and the plant 

 dies down to an underground stem, and behaves as a 

 pronounced xerophyte. 



Tropophytes (Gr. tropos, change). — ^The great majority 

 of our plants are tropophytes. Unlike evergreens, they 

 exhibit one set of characters in summer and another 

 during winter. They provide against drought by 

 changing their mode of life at the approach of winter 

 (see Chapter VI.). 



