Tropical Forests 
east coast of America have been carried right across the 
Atlantic to the West African shore, for there are two 
distinct mangrove associations. One occupies the shores 
of the Pacific and Indian Ocean, and the other occurs on 
both sides of the Atlantic. 
But where mangroves have established themselves, 
they are of very great importance as land-formers, Mud- 
and sand-banks are first colonised by Rhizophora or 
Brugueira, whose seedlings can also float for a long 
time (117 days). Then the other mangroves assist to 
form the usual swamp, with its “dense dark wall of 
foliage, from which the light is reflected.” 4 
As time goes on, the mangrove pioneers are always 
annexing new territory from the sea, whilst further in- 
land the level of the mud is slowly rising by the regular 
deposits at every tide. When the salt-water no longer 
reaches their roots with every tide, the mangroves 
begin to be unhealthy and give place to other trees and 
shrubs. 
Whether this is because the mangroves require a daily 
salt-bath for health, or because they cannot compete with 
these plants of ordinary soil, does not seem to be quite 
understood. 
The first invaders of the mangroves are for the most 
part certain special transitional forms of trees, shrubs, 
and climbing plants. 
Their reign is, however, soon terminated by the in- 
vasion of the tropical forest, which in the end covers 
with dense jungle what was once estuarine mud, and 
which may be cleared away for oil-palms, for rice-fields, 
or other valuable plantations. 
1 Von Faber. 2 Ule, Spruce. 3 Gadow. * Von Faber, 
5 Vaughan-Cornish. ® Cantlie. * Colonial Reports Misc., No. 51. 
8 Schimper, Guppy. See also Engler. 
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