274 OUTLINE OF PLANT GEOGRAPHY 



The "campoe" or savannas, open grassy or scrubby districts, 

 occupy but a small part in the valley proper, but north and south 

 merge into the great llanos or prairies of Venezuela and Argentina. 



Comparing the different types of the Brazilian forest Spruce 

 makes the following statement: 1 "And yet when the constituent 

 plants of the different classes of forest come to be compared to- 

 gether, they are found to correspond to a degree quite unexpected; 

 for although the species are almost entirely diverse, the differences 

 are rarely more than specific. It is only in the caatingas that a 

 few genera, each including several species, seem to have taken 

 up their exclusive abode; such are Commianthus among Rubiaceae, 

 Bugamea among Loganiaceae . . . and there are a few other 

 peculiar genera, chiefly monotypic. But of the riparial plants 

 nearly every species has its congenor on terra firma to which it 

 stands so near that, although the two must of right bear different 

 names, the differences of structure are practically such as might 

 have been brought about by long exposure even to the existing 

 state of things without supposing them to date from widely dif- 

 ferent conditions in the remote past; this is especially true of such 

 genera as Inga, Pithecolobium, Lecythis, and of many Myrtles, 

 Melastomes and Sapotads, etc." 



Some characteristic species are very wide-spread. Thus Spruce 

 mentions the Brazil nut (Bertholletia excelsa), perhaps the finest 

 and most characteristic tree of the virgin forest. It grows almost 

 throughout the Amazon valley where the soil is suitable, from 

 Para to a point more than 1,200 miles west on the Amazon proper, 

 and for many hundred miles up its principal affluents and the 

 regions of the upper Orinoco. One of the finest palms, Maxi- 

 miliana regia, with huge leaves 30-40 feet long, is even more wide- 

 spread. 



As a rule, however, the most wide-spread species do not belong 

 to the heavy forest, but to the open savanna. 



Very often a species restricted to a somewhat limited area, is 

 replaced elsewhere, under similar conditions by a similar, but 

 distinct spec] 



Two types of rivers are found in the Amazon system, clear or 

 " black " rivers of which the Rio Negro is the type, and the " white," 

 or turbid rivers like the Amazon itself. The riparian vegetation 



1 hoc. cit. 



