58 BRITISH PLANTS 
xerophytic form which will suffice to carry them safely 
through the winter. These are tropophytes (p. 31), a 
type of plants well suited to a country like ours, and 
prevalent in all regions outside the Tropics. 
The least that any tropophyte can discard are its 
summer leaves ; shoots may also fall, and the destruction 
of summer organs may be carried so far that all the 
vegetative parts above ground may perish, and only 
specialized underground organs survive (pp. 62, 110). The 
perennial parts of tropophytes are always xerophytic. 
In summer, tropophytes, like other plants, are variously 
circumstanced with regard to water. Some live in moist 
habitats, others in dry. If water is abundant at all 
times, the summer characters are hygrophytic ; if water 
is deficient, xerophytic characters dominate. Between 
the two extremes lie a host of mesophytic forms with no 
marked features either way ; the water-supply is adequate, 
and the drought is seldom sufficiently prolonged or intense 
to cause them much damage. 
According to the nature of the swmmer environment, 
tropophytes are divided into three groups : 
1. Hygrophilous Tropophytes, which, during summer, 
are surrounded by constantly moist conditions; the 
annually-renewed foliage and shoots exhibit only hygro- 
phytic characters—e.g., marsh-plants. 
2. Mesophilous Tropophytes.—The great majority of 
tropophytes are included in this group—e.g., deciduous 
trees and bushes, herbaceous perennials, and most annuals 
and biennials. 
3. Xerophilous Tropophytes.—These are tropophytes 
which during the vegetative season live in physically or 
physiologically dry places—e.g., sand-dunes, sea-beaches. 
They show one kind of xerophytic characters in “‘ sum- 
mer ”’ and another kind during “‘ winter.” But, however 
bad the summer conditions may be, the winter conditions 
are worse, for then cold is added to the other factors 
reducing absorption. If the xerophytic characters present 
during summer are not sufficiently pronounced to secure 
safety to the plant in winter, they must be discarded, 
and a more suitable habit adopted. The most important 
representatives of this group are : 
1. Succulent seaside - annuals—e.g., glasswort (Sali- 
cormia herbacea), sea-blite (Sueda maritima), ete. 
