460 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



amount of salt, are inclined to be highly characteristic and only 

 gradually, in space or in time, able to take on the aspect of the local 

 hinterland clim.ax. Often they develop as a belt just inland of the 

 mangrove. In other places the forest or scrub even in the tract 

 lying nearest to the sea may be devoid of halophytic species. Where 

 salinity prevails and the littoral forest differs from that of the general 

 hinterland, the sandy or stony soil is often almost bare of dead leaves, 

 and the trunks of the trees are commonly naked ; or they may be 

 beset with epiphytes, both thick-leafed and cryptogamic, and support 

 a mass of thin-stemmed climbers. Where the trees are less close 

 together, there is often a dense undergrowth of shrubs and small 

 trees, or patches of coarse Grass. The leaves are usually leathery 

 or succulent, often hairy when young, or hard and sword-like in 

 the cases of Screw-pines and the leaf-segments of Coconut {Cocos 

 micifera) or other Palms. Particularly characteristic trees in such 

 situations in the Old World are species of Baningtonia. As the 

 distance from the coast increases, protective measures become less 

 necessary and pronounced, and the forest takes on more and more 

 the appearance and flora of the local climax, containing fewer and 

 fewer species which are not to be found away from the influence 

 of the sea. In other instances the littoral forest may be deciduous, 

 or dominated largely by a single species (such as Ironwood, Casuarina 

 equisetifolia). The proximity of the sea is also expressed in the 

 buoyancy of many of the seeds and fruits, which are commonly 

 found in sea-drift, and which help some at least of the characteristic 

 species to attain a very wide distribution. This is said to be the 

 case with the Coconut, plants of which form such a characteristic 

 feature of many tropical sea-shores (Fig. 160). 



Further Seral or Edaphic Communities 



Apart from various seral types already mentioned, such as the 

 dunes and, presumably, littoral woodlands dealt with in the last 

 section, and biotic plagioclimaxes which in some respects are of a 

 seral nature, there are yet others to consider in tropical and sub- 

 tropical regions. Outstanding are various types of forested and 

 reedy swamps, secondary scrubs and forests, and weedy com- 

 munities of many kinds. 



Swamps occur chiefly around the edges of quiet bodies of fresh 

 water, in sheltered arms of lakes or sluggish rivers, and in filled or 

 filling hollows where the ground is at least waterlogged and where 



