46 SYLVICULTURE IN THE TROPICS 



PT. I 



low country of Ceylon and Java. It has also been 

 stated that on the central African plateau and in parts 

 of South America the dense forest is confined to the 

 watercourses, the higher ground being covered by steppe 

 or savannah or open forest. There are some other 

 peculiarities of forest vegetation caused by the presence 

 of water which deserve some special mention. 



On the sea-shores of the Tropics, in regions where 

 the rainfall is also abundant, the estuaries of rivers, 

 backwaters, and lagoons, which are covered with water 

 at high tide and are left exposed to the air during low 

 tide, there is to be found a type of forest known as 

 "Mangrove Swamps," which has some peculiar char- 

 acteristics. Most of the trees require a certain amount 

 of fresh water in order to be able to live, but some may 

 live in undiluted sea-water, as e.g. Rhizophora mucron- 

 ata} Many of the trees growing in the black mud of 

 these swamps support themselves by stilt-like roots 

 which spring out of the stems and, even in the case of 

 the tree mentioned above, from the branches. They 

 are thus able to support themselves in the liquid mud 

 from which they spring. In order that the roots may 

 be supplied with the oxygen which they require, they 

 give out curious negatively geotropic branch roots,* 

 known as pneumatophores, which emerge from the mud 

 in the shape of pointed cones, or " knee-roots," provided 

 with lenticels, stomata, or part excortication, in order to 

 take up the oxygen at low tide. The foliage of these 

 trees is generally thick and fleshy, and the fruit starts 

 germinating before it falls from the tree. In the case 

 of the true Mangroves {Rhizophora, Bruguiera, and 

 Ceriops) the radicle goes on lengthening until it is 

 sometimes the length of the arm. As it is more or less 

 pointed, and the lower end is heavier than the plumule 

 end, the seedling remains upright when it detaches itself 

 from the tree and fixes itself vertically into the soft mud, 

 into which it at once proceeds to send out roots to 

 establish itself. The most important natural order in 



1 Schimper, op. cit. p. 396. 



