280 OUTLINE OF PLANT GEOGRAPHY 



leaves, usually woolly beneath, are suggestive of the castor-bean. 

 The Cecropias are everywhere abundant and conspicuous in the 

 wet American tropics. 



The myrtle family is an important one in tropical South America, 

 and comprises many species of Eugenia, Myrcia, Psidium, and 

 others. Several species of the latter genus, yield the well-known 

 guavas, now extensively cultivated in most tropical and some sub- 

 tropical countries. 



Among the giants of the Amazonian forest are the silk-cottons 

 (Bombax, Ceiba) whose huge trunks are supported by enormous 

 buttress-roots. The silky down attached to the seeds of some 

 species furnishes the silk-cotton or " Kapok" used for stuffing 

 mattresses and similar purposes. 



Of the many trees yielding useful commercial products, the Para 

 rubber (Hevea Braziliensis) takes first place, and until quite re- 

 cently was the most important export from Brazil. It belongs to 

 the Euphorbia family, and is a tree of moderate size with trifoliate 

 leaves, something like a Laburnum. It grows in the low forest 

 over much of the Amazon valley, and now is cultivated on a great 

 scale in many tropical countries, but with especial success in various 

 parts of the Malayan regions, where the plantations furnish most 

 of the rubber requirements of this age of automobiles. Another 

 large and common tree of the same family, the " sand-box" (Hum 

 crepitans) is abundant in the virgin forest. 



The custard-apples (Anonaceae), and the sapodillas (Sapota- 

 ceae), include many important fruits of the Amazonian region, 

 some of the latter also furnishing that remarkable substance 

 "chicle," the basis of one of America's noblest products, chewing 

 gum. 



The Brazil nut represents the purely tropical family Lecythi- 

 daceae, especially developed in northern Brazil, while the " Spanish 

 cedar" (Cedrela spp.), and species of nutmeg (Myristica spp.), are 

 also characteristic of the old world tropics. 



These are but a few samples of the thousands of species of trees 

 that make up the great equatorial American forest. 



Palms are much more conspicuous than in most parts of the 

 eastern tropics. Whether the number of species is greater might 

 be questioned; but as regards conspicuous arborescent species, 

 there is no question that the American tropics surpass any part of 



