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 summer 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. The^e 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- 

 c ornia herbacea), sea-blite (Sueda maritima), etc. 



