CLIMATOLOGY OF THE PERUVIAN ANDES 151 



that wooden nails are made from it; and the rarer sandy matico, 

 highly prized for dug-out canoes. Also from the chunta palm, hol- 

 low except for a few central fibers, easily removed, pipes are made 

 to convey water. The cocobolo has a rich brown color and a 

 glossy surface and is very rare, hence is much sought after for 

 use in furniture making. Most of these woods take a brilliant 

 polish and exhibit a richness and depth of color and a beauty of 

 grain that are rare among our northern woods. 



The plains forest northeast of the mountains is in the zone of 

 moderate rainfall where there is one long dry season and one 

 long wet season. When it is dry the daytime temperatures rise 

 rapidly to such high levels that the relative humidity of the air 

 falls below 50 per cent (Fig. 110). The effect on the vegetation is 

 so marked that many plants pass into a distinctly wilted condi- 

 tion. On clear days the rapid fall in the relative humidity is 

 astonishing. By contrast the air on the mountain border heats 

 more slowly and has a higher relative humidity, because clouds 

 form almost constantly in the ascending air currents and reflect 

 and absorb a large part of the heat of the sun's rays. It is strik- 

 ing to find large tracts of cane and bamboo on the sand bars and 

 on wet shady hillslopes in the slope belt, and to pass out of them 

 in going to the plains with which we generally associate a swamp 

 vegetation. They exist on the plains, but only in favored, that is 

 to say wet, spots. Larger and more typical tracts grow farther 

 north where the heavier rains of the Amazon basin fall. 



The floods of the wet tropical season also have a restricting in- 

 fluence upon the tropical forest. They deliver such vast quantities 

 of water to the low-gradient lowland streams that the plains 

 rivers double, even treble, their width and huge pools and even 

 temporary lakes form in the shallow depressions back of the 

 natural levees. Of trees in the flooded areas there are only those 

 few species that can grow standing in water several months each 

 year. There are also cane and bamboo, ferns in unlimited num- 

 bers, and a dense growth of jungle. These are the haunts of the 

 peccary, the red forest deer, and the jungle cat. Except along the 

 narrow and tortuous animal trails the country is quite impassa- 



