136 SOUTH AMERICA 



in the whole world more favourable to vegetation than 

 that which the Amazon plain provides, and we may 

 regard its luxuriance as the supreme effort of plant-life 

 at this period of the world's development. This is 

 expressed in the indescribable wealth of tree growth, 

 in the forest "par excellence, called by Humboldt 'hylea', 

 and by the Portuguese the ' selva '. 



The vegetation, monotonous though it appears to the 

 traveller, has been divided into a number of charac- 

 teristic formations or associations. 



Flood Forests. The banks of the streams, periodical ly 

 flooded and having an excess of water, are characterized 

 by a peculiar type of forest called the 'igapu' or 

 'caa-gapu' (the rebalsa of the Spaniards), extending 

 as a broad fringe bordering on the rivers. It finds 

 an exact replica in the flood-forests of the lowlands 

 of the Mekong (Siam) and in the sundarbans of the 

 mouth of the Ganges From the slimy, hardly solid 

 mud has sprung a rank and dense growth of tall 

 trees overgrown with a continuous drapery of lianas, 

 thus forming an unbroken dark canopy, a green wall 

 impenetrable from outside. It forms a gloomy, stifling, 

 musty, shady, damp vault, supported by innumerable 

 pillars, and choked with a perfect tangle of climbers 

 inside. The plants, simply gorged with water, but 

 feebly rooted in the mud, support each other, tied 

 together by the lianas. This igapii is remarkable for its 

 wealth in palms and its poverty in flowers, and is 

 particularly well developed on- the innumerable sluggish 

 side canals or 'igarapis' that intersect it. When the 

 rivers are in spate its canopy simply rests on the water. 

 It is the home of the Para rubber-tree (Hevea brazi- 

 liensis or seringeira), the tapping of which gives em- 

 ployment to a roaming, half -wild, and scattered population 



