54 THE GEOGRAPHY OF PLANTS. 



rises from the root-stock to a height (often) of six- 

 teen feet without a joint, and of equal thickness 

 throughout. The first joint then occurs, and the 

 first branchlets are formed. A joint then appears 

 at every fifteen or eighteen inches, to a further 

 height of forty to fifty feet. The whole stem is 

 from fifty to sixty feet high, but the weight of 

 the numerous branchlets forces the slender stem 

 to droop, and the upper part describes an arch, 

 which adds greatly to its graceful appearance. 



Two kinds of mandioc, or cassava, grow 

 in Spanish America and Brazil, which bear 

 tuberous roots, the farina of which is used 

 as food by the natives ; the root of one is harm- 

 less, but the other contains a poisonous milky 

 juice, the effects of which are removed by 

 cultivation or pressure. Its limit of growth 

 extends to about 30 on each side of the 

 equator, and an acre of it is said to yield as 

 much nutriment as six acres of wheat. The 

 humiria (a native of South America) has so 

 powerful a perfume, that it has been inhaled at 

 the distance of three miles out at sea. 



We have already mentioned palms as among 

 the characteristic plants of this zone. There 

 are no less than four hundred known species of 

 this remarkable and beautiful tribe, eighty-one 

 of which inhabit tropical Brazil alone ; some 

 with hardly any stem, others towering to the 

 height of one hundred and thirty feet. So 

 narrow here are their geographical limits, that 

 Humboldt and Bonpland discovered a new 

 species in every fifty miles of travelling. The 



