TROPICAL DISTRICTS CONSTANTLY MOIST zHr. 



:> 



On the whole, the vegetation of the constantly humid districts is clearly 

 marked off from that of the periodically dry districts. Constantly humid 

 \'Ustricts, whenever undisturbed by cultivation, are nearly always covered with 

 evergreen rain-forest ; periodically dry districts are occupied by deciduous 

 zi'oodland and savannah. If precipitatioji be very slight even during the 

 rainy season, the character of vegetation becomes that of desert. 



Hann's tropical district without a dry season includes, passing from east 

 to west: I. In Australia, New Guinea with its neighbouring archipelagos, 

 the Bismarck and Solomon Islands, and most of the Pacific islands. 2. In 

 \Asia, the Philippines, the Moluccas (for the most part), West Java, Celebes, 

 iRorneo, Sumatra, and the southern end of Malacca. 3. In Africa, the 

 Mascarenes, Eastern Madagascar, Zanzibar with the neighbouring conti- 

 fiental coast, and the district of the great African lakes. 4. In America, 

 |the Brazilian coast district to the south of 15° S., the northern part of 

 the basin of the Amazon, Guiana, the Lesser Antilles (for the most 

 part), and the east coast of Central America. 



In general, the boundaries of the district designated above coincide 

 with those of the tropical rain-forest. Wherever it has not been cleared, 

 the tropical rain-forest covers the lowlands and ascends the highlands as 

 far as the tropical climate extends. Here and there the tropical rain-forest 

 lightly oversteps the boundaries of the tropical climate proper, both in the 

 horizontal and vertical directions. Tropical rain-forest also occurs within 

 the range of the district with marked dry seasons, chiefly among mountains 

 that condense moisture, in districts of limited extent, where the climate 

 is constantly humid and occasions the appearance of the rain-forest, as in 

 the eastern Himalayas, in Burma, on the western slopes of the Nilgiris, 

 in West Ceylon, in Kamerun, and on the cast coast of tropical 

 Australia. 



A similar, but usually less luxuriant, evergreen forest frequently, but not 

 always, fringes the rivers of the periodically dry district. Such fringing 

 forests, as has been already stated, are independent of atmospheric 

 precipitations and will be discussed in the chapter dealing with the 

 edaphic influences. 



2. GENERAL CHARACTER OF THE TROPICAL 

 RAIN-FOREST. 



i. EXTERNAL ASPECT OF THE FOREST. 

 When the rain-forest is viewed from outside, say from a ship sailing by 

 a forest-clad coast, or from the summit of an elevated point rising above 

 a tract of forest, many distinctions between it and forest in temperate 

 regions meet the eye. The upper surface never exhibits a uniform tint, 

 but forms a richly varied mosaic, in which every shade of green is 

 represented : least frequent of these is the fresh green, say like that of 



