460 A TEXTBOOK: OF GENERAL BOTANY 
passages for the aération of the roots. In other cases the shallow 
water is occupied by a growth of shrubs or trees. Salt-water 
swamps in temperate regions are occupied by a reedlike growth 
consisting largely of monocotyledonous plants. In the tropics — 
mangrove-swamp forests are formed on mud flats, which are 
exposed at low tide and at high tide are covered by salt water. 

Fig. 516. Interior of Philippine mangrove swamp at low tide 
Note the aérating prop roots of Rhizophora and the erect aérating roots which 
project upward out of the mud 
Mangrove-swamp forests. The term mangrove-swamp forest is 
applied to the type of forest occurring on tidal.flats along trop- 
ical seacoasts (Figs. 197, 516). The conditions most favorable 
to their development are found in quiet bays into which flow 
large rivers whose lower reaches have little fall. The descending 
waters of the rivers are checked when they meet tidewater, and 
deposit their sediment in the form of broad flats or deltas near 
the mouths of the rivers. These flats are usually cut by a net- 
work of channels through which the advancing and receding water 
