14] VEGETATIONAL TYPES OF TROPICAL LANDS 457 



mud ^ if the tide is out — and forms anchoring lateral roots in a matter 

 of hours, often continuing to grow in situ. Actually the seedling is 

 buoyant, so that if the tide is in or for some other reason the root 

 does not stick sufficiently in the mud when it drops, it may be 

 transported by water to some other situation, there to resume normal 

 growth if conditions are favourable. Young seedlings are seen 

 growing in fair numbers among the roots in the foreground in 

 Fig. 158. 



Mangroves often extend some distance inland in brackish swamps 

 and lagoons, forming a fairly continuous fringe, or occupying islets 

 between which run the sluggish tidal streams. At high tide they 

 appear like a flooded forest or, about their low and tangled margins, 

 like a mass of green or greyish foliage sitting on the water. Some- 

 times thev are replaced bv Palms (such as Nipa friiticans) or other 

 large monocotvledonous plants, while near their climatic limits they 

 tend to form dense tall thickets rather than forests. Recession of 

 the tide even in the forested tvpes reveals an ungainly mass of muddy 

 roots and often grotesque boles. Even the trees are liable to be 

 mis-shapen and lowly, while bubbles of stinking gas rise from the 

 rotten mire, and a teeming population of crawling creatures adds to 

 the atmosphere of gloomy squalor. 



The climate is usually hot and humid, and conditions are kept 

 monotonous by the tides and salinity, though there may be alternat- 

 ing heavy rainfall and scorching sun. The dominants are evergreen 

 and halophytic, the foliage being leathery, fleshy, or protected by 

 a glossy exterior or wooUv covering against excessive transpiration. 

 Their growth is often so manifestly dense as seemingly to prevent 

 the entrance of herbaceous or other vascular plants, though indeed 

 there are few of these which are adapted to the very specialized 

 habitat. A dark coating of Red Algae may occur on the stems and 

 roots submerged by the tides, and some Lichens are usually to be 

 found on the stems well away from the water ; but other epiphytes 

 are rare. 



The chief development of mangroves is in southern and eastern 

 Asia, with extensions to northern Australia and the Pacific. Man- 

 groves also occur about Central America, and, to the east, with 

 little variation on both sides of the Atlantic. In areas of low pre- 

 cipitation and general aridity, mangroves and other maritime wood- 

 lands are usually lacking or only poorly developed, even as are 



^ According to Dr. Frank E. Egler {voce), this happens far less frequently than 

 the text-books imply. 



