always be found a small distance in from the shore. There 
is a band, then, where the two species are somewhat con- 
tiguous. Hevea Spruceana is often found along the edges 
and in the interior of these islands where the soil is less 
sandy and where a muddier condition indicates more 
organic residue. H. Spruceana, H. microphylla and H. 
Benthamiana are frequently seen in a contiguous distri- 
bution, but I have never found these three or Hevea 
microphylla occurring with any of the other species in a 
mixed stand. 
This island type of habitat is found, for the most part, 
from the mouth of the Rio Curicuriari downstream, pro- 
bably merely because the islands above this point are 
smaller and almost always rock bound with little, if any, 
floodable area. There are, however, some small islands 
in the Rio Uaupés where the seringueira tambaqui is 
reported. 
In the middle Rio Negro the same type of distribution 
found on the islands often obtains where the banks of 
the mainland are low and comprise flood land. At Nibart 
and Piloto, for example, a visit to the banks along the 
river in the vicinity of the islands which are rimmed with 
Hevea microphylla showed that in certain sandy stretches 
along the shore itself and near the mouth of sandy creeks 
—wherever deep muddy silt was not abundant—this 
species was common. At Nibart, I estimated a density 
of about four or five trees per hektar at the mouth of a 
creek on the right bank directly opposite the Ilha de 
Xibart. 
In the upper Rio Negro, we can find Hevea micro- 
phylla along the main bank of the river itself, and inland 
along low and sluggish creeks to a rather appreciable 
distance. The main affluents of the Rio Negro also have 
stands of Hevea microphylla at appropriate sites along 
their banks and near the mouth of creeks. The greatest 
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