AMAZONIAN VEGETATION 357 
to have taken up their exclusive abode : such are 
Commianthus among Rubiacese, Pagamea among 
Loganiaceae, Myrmidone and Majeta among Melas- 
tomaceae ; and there are a few other peculiar genera, 
chiefly monotypic. But, of the riparial plants, 
nearly every species has its congener on terra 
firme, to which it stands so near that, although 
the two must of right bear different names, the 
differences of structure are precisely such as might 
have been brought about by long exposure even 
to the existing state of things, without supposing 
them to date from widelv different conditions in 
the remote past ; and this is especially true of such 
genera as Inga, Pithecolobium, Lecythis, and of 
many Myrtles and Melastomes, Sapotads, etc. 
As an illustration of the features which tend to 
impress a certain character of uniformity on the 
vegetation of the Amazon region, I will take the 
case of a single tree, Bertholletia excelsa (H. and B.) 
— perhaps the noblest tree of the Amazon region, 
and the most characteristic of its Virgin Forests — 
and briefly sketch its distribution. In aspect and 
foliage it is not unlike a gigantic Chestnut tree ; 
and the seeds (the Para nut of commerce), if not 
much like chestnuts in their trigonous bony shell, 
are not very different in taste, whence the Brazilian 
name of the tree, " Castanheira," and of the seeds 
" castanhas." This tree is found almost throughout 
the Amazon valley, both to north and south, chiefly 
wherever there is a great depth of that red loam 
which it pleases M. Agassiz to call "glacial drift." 
About Para itself there is no lack of it, especially 
in the fine woods of Tauaii ; and 1200 miles farther 
to the west it may be seen in some abundance on 
