6 $2 



ZONES AND REGIONS [Pt. Ill, Sect. II 



temperate zones differ in essential points from those of the tropics, and 

 especially heaths and moors, which do not occur in tropical climates. 



%. TEMPERATE LITTORAL FORMATIONS. 

 The coasts of temperate seas afford to plants habitats just like those in 

 the tropics : rocky, sandy, clayey banks, areas that are always dry and 

 areas that are flooded at high tide. On the other hand, the type of vegeta- 

 tion corresponding to the different habitats is much less diversified, since 

 continuous woodland — in particular the mangroves, so widely spread in the 



Fig. 392. Swamp-forest in Louisiana. Tree-trunks expanded at the base. The branches 

 hung with Tillandsia usneoides. From a photograph. 



tropics — is absent owing to the strong wintry winds ; and, as a rule, woody 

 plants are low, scattered shrubs. 



The clay and clayey loam which is flooded at high tide, and which in the 

 tropics forms the substratum of the majority of mangroves, in temperate 

 shores is clad with vegetation only in estuaries and lagoons. In Central and 

 Northern Europe the first settler in such littoral swamps is Salicornia her- 

 bacea (Fig. 396), a succulent herb the marked xerophilous structure of 

 which corresponds to the highly saline nature of the substratum. By the 

 Mediterranean other shrubby species of Salicornia (S. fruticosa, S. macro- 



