CHAPTER VI 

 EDAPHIC INFLUENCES IN THE TROPICS 



i. Edaphic Influences in Tropical Inland Country, i. Laterite. Physical and 

 chemical properties. Effects on vegetation. Eng-forest in Burma, ii. Lime. Unfavour- 

 able influence on vegetation in the tropics. Occurrence of thorn-forest on calcareous 

 soil. iii. Humus. Its relatively slight development in the tropics. Regur in South 

 India. Absence of peat-formation, iv. Siliceous Soil. Sal-forest of India. Bamboo- 

 forest, v. Swampy Ground. Palm-woods. Swamp-forest in Burma. Swamps with- 

 out forest, vi. Fumaroles in Java. Xerophilous vegetation. 2. Formations of the 

 Tropical Sea-shore. i. Classification of Tropical Littoral Formations. ii. Open 

 Formations of the Sandy Shore. Pes-caprae formation. Littoral shrubs. Pandanus. 

 iii. Littoral Woodland above High-tide Mark. Its occurrence in the Malay Archipelago, 

 in Pegu, in East Africa. Oecological characters. Casuarina-forest. iv. Woodland Forma- 

 tions below High-tide Mark. Mangrove or tidal woodland. The Eastern mangrove. 

 Characteristic plants. Oecological characters. Rhizophora mucronata. Vivipary and 

 germination in Rhizophoraceae, Aegiceras, and Avicennia. Habit of mangrove-plants. 

 Stilt-roots. Pneumatophores. Physiognomy of the mangrove-forest in South Java. 

 Nipa-formation. Transition to the inland formations. The Western mangrove, v. Dis- 

 tribution of Littoral Formations in the Tropics. 



i. EDAPHIC INFLUENCES IN TROPICAL 

 INLAND COUNTRY. 



The differentiation in the flora and in the oecological features of the 

 vegetation, arising from differences in the constitution of the soil, is much 

 more pronounced in the periodically dry districts than in the constantly 

 humid ones, where the rain-forest, without apparently exhibiting any 

 essential difference, extends over the most varied kinds of soil and shows 

 a different physiognomy only in those stations that are swampy or very 

 rich in salts. 



Owing to the lack of proper observations, it is not at present possible to 

 distinguish between the physical and chemical influences of the soil in the 

 tropics, and the whole subject of edaphic influence is still very little studied, 

 except in regard to littoral formations, so that we must be satisfied by 

 considering individual kinds of soil and the vegetation peculiar to each, 

 without inquiring closely into causes. 



