128 PLANT GEOGRAPHY 



Host, is dominant. The name of a formation is made 

 by the suffix -ion, and that of the chief association can 

 be added in the possessive. A sand-dune being known 

 as an Arenarion, a particular sand-dune may beArenarion 

 Caricis-arenaricB. For all the similar formations in the 

 world the term federation has been proposed. 



GUILDS. Plants dependent upon others, such as 

 lianes, epiphytes, saprophytes, and parasites, though 

 they cannot well be dominant, may constitute a marked 

 feature in an association. For societies of such plants 

 the term guild has been suggested. 



ZONATION. Within the limits of one formation, pro- 

 gressive changes in habitat from place to place often 

 produce a marked grouping of plants or associations in 

 zones. A salt-marsh formation, for example, as traced 

 from the sea landwards may exhibit in succession a 

 Salicornietum herbace<z, an Atriplicetum, a Cakiletum, 

 and a Triticetum juncei, associations, that is, in which 

 Glass-wort, Crab-weed, Sea-rocket, and Triticumjunceum 

 L. are dominant. Similar horizontal zonation is seen 

 on the banks of rivers and ponds (Fig. 14). In forests, 

 woods, and thickets a vertical zonation or succession 

 of " storeys " may be traced. Thus we may have the 

 " ground-storey," mainly occupied by cellular crypto- 

 gams, within two inches of the ground; the "field- 

 storey," mainly composed of grasses and herbaceous 

 plants, up to thirty-six inches; the " shrub-storey," and 

 the " tree-storey." The seasonally complementary asso- 

 ciation of Endymion, Pteris, and Holcus previously 

 mentioned (p. 57) may be considered as a form of 

 vertical zonation. 



TROPICAL FORMATIONS. So potent are climatic in- 

 fluences that striking differences distinguish the associa- 

 tions and formations of the three or four great latitudinal 

 regions. In most, however, woodland, grassland, desert, 

 and shore are represented. The Tropical Rain-forest, 

 in which the dominance of any one species can seldom 

 be detected, is characterised, as we have seen, by a 

 profusion of species, especially lofty evergreen trees with 

 glossy leathery leaves, woody lianes, and epiphytes. 

 Within the limits of the tropophilous Monsoon-forest 

 local differences show themselves, as in the Bamboo- 

 forest of the cloud-belt, the Sal forest of India, in which 

 Shorea robusta Gaertn. is dominant, on permeable 



