THE NEOTROPICAL REGIONS 273 



While there is an immense number of species there are certain 

 general resemblances throughout the great Amazonian forest area. 

 Thus while the species of the different types of forest, riparian, 

 upland and dr} r , are mostly different, the genera are largely the 

 same, and some of the most important species occur over a very 

 large extent of country. 



The riparian forests, or gapo, are flooded for long periods, and 

 the members of this association must necessarily be such species as 

 can endure this unusual condition. The trees of the gapo are rarely 

 as tall as those of the virgin forest which lies above the high-water 

 mark, but the two formations merge into each other at the upper 

 limit of the gapo whose outer margin is composed of low shrubs 

 and bushes, and many aquatics, like arums, rushes, sedges, etc. 



The gapo is notable for the great variety and abundance of 

 palms, many of which overtop the other forest trees, and sometimes 

 occur in groves forming long avenues of columnar trunks along 

 the shore. 



When the water recedes, the gapo develops a dense undergrowth 

 of herbaceous plants, and every tree and shrub is draped with a 

 curtain of herbaceous creepers, passion-flowers, morning glories, 

 and others, often having flowers of great beauty. 



The virgin forest is distinguished by the very tall and closely set 

 trees, whose lofty trunks, often with great buttresses at the base, 

 support a thick canopy of foliage which shuts out most of the light. 

 so that there is relatively little undergrowth, except young trees 

 of the predominant species, and slender palms which earn' their 

 crown of leaves toward the light. Stout lianas, like cables looped 

 from tree to tree, belong to many species, but their foliage and 

 flowers, borne high up in the tops of the trees, are rarely recogniz- 

 able from the floor of the forest. This virgin forest covers an 

 enormous area in the Amazon valley, the gapo, of course being 

 confined to the lowland area subject to the annual inundation. 



The "caatinga" open or white forest, occupies areas of poor 

 soil in the drier districts, and is composed of low trees and shrubs, 

 with few lianas and palms, the latter when present being peculiar 

 forms, quite distinct from those of the wel forest. 



To these might be added the second growth forests, where a 

 tangle of trees and shrubs fight with each other for the possession 

 of the soil. 



