INFLUENCE OF WATER ON PLANT-LIFE 29 
1. Hygrophytes (Gr. hygros, moist; phyte, plant), 
plants adapted to very moist conditions. 
2. Xerophytes (Gr. veros, dry), plants adapted to live 
in a dry soil or under conditions unfavourable to their 
development, at least during a part of the year. The 
conditions may all be ultimately referred to the quan- 
tity, availability, and usefulness of the water -supply 
(Chapter IV.). A wet soil is dry if the plant can absorb 
none of the water. 
3. Mesophytes (Gr. mesos, middle, intermediate), plants 
occupying an intermediate position with regard to water. 
1. Hygrophytes. 
True hygrophytes are plants which live in places always 
moist, and which, during the whole year and the whole 
of their lives, exhibit characters adapted to moist con- 
ditions. The extreme hygrophyte lives in an atmosphere 
saturated with moisture. It cannot transpire, but the 
transpiration-current is kept going by the elimination of 
water in liquid drops through hydathodes (p. 27). More- 
over, such plants can only live in regions where no un- 
favourable season intervenes to disturb their develop- 
ment. Winter-cold means drought even for a hygrophyte 
(p. 64). For this reason they are only found in the wet 
parts of the Tropics, where there is no dry season and 
no winter. They are evergreen, and live in the shade 
of trees or dripping rocks. Outside the Tropics they are 
only found in very damp, shady places where frost is 
unknown. In the British Isles the nearest approach to 
these conditions is found in the extreme south-west of 
Ireland, and the plants which, in their characters, most 
nearly resemble true hygrophytes are the Filmy Ferns. 
The Killarney fern, for example, is a plant with delicate 
evergreen leaves, and lives in wet, sheltered crannies 
in the rocks near the Lakes of Killarney. Elsewhere 
in this country they can only be reared in glass cases, 
which are shaded from the sun, and in which the air 
is kept constantly saturated with moisture. 
The leaves of many of our marsh and wet-meadow 
plants exhibit hygrophilous (Gr. hygros, moist ; phileo, 
I love) characters in summer ; but as they perish at the 
