HALOPHYTE SOCIETIES. 253 



difficulty that means impossibility to all but the compara- 

 tively few forms that have succeeded in living in halophyte 

 conditions. 



Numerous halophyte societies have been recognized, but 

 attention is called only to a few. 



170. Mangrove swamps. This is certainly the most vigor- 

 ous of the halophyte societies. Mangrove swamps occur 

 along flat tropical sea coasts, where the waters are quiet. 

 The mangrove is a tree of curious habit, which advances 

 slowly out into the water and extends back landwards as 

 low woods or thickets (see Figs. 204, 205). The whole 

 surroundings appear forbidding, for the water is sluggish 

 and mucky, covered with scum, rich in bacteria, and with 

 bubbles constantly breaking upon the surface from decay- 

 ing matter beneath the water. The mangrove has the pe- 

 culiarity of germinating its seeds while still upon the 

 tree, so that embryos hang from the trees, and then drop 

 like plumb-bobs into the muck beneath, where they stick 

 fast and are immediately in a condition to establish them- 

 selves. In these mangrove swamps the species are few, and 

 the adaptations chiefly in the way of developing various 

 kinds of holdfasts for anchoring in the uncertain soil, and 

 also various devices for carrying air to the submerged parts. 



171. Beach marshes and meadows. The salt marshes and 

 meadows near the seacoast are very well known. They 

 lie beyond the reach of ordinary flood tide, but the waters 

 are brackish. In these marshes and meadows occur certain 

 characteristic halophyte grasses and sedges. Such forms 

 being the dominant type give the general appearance of 

 a coarse meadow. The difference between a marsh and 

 meadow is simply a question of the amount of water. 



172. Salt steppes. These areas are often large in extent, 

 and belong to the interior of continents (see Fig. 206). 

 So far as water supply is concerned, they hold the same 

 relation to other halophyte societies as do the plains to 

 mesophyte societies. In the United States one of the most 



