THE HEVEA RUBBER TREE IN THE AMAZON VALLEY 53 
Table 13. — Measurements of carpel lengths of Hevea fruits in Bolivia and Brazil 
Tree 
Carpel 
length 
(mm.) 
Tree 
Carpel 
length 
(mm.) 
Tree in square at Cobija, Bolivia - 
Hevea randiana, Museu Goeldi, Para... 
/ 38.5 
\ 38.5 
f 37 
38 
39 
39 
37 
37 
38.5 
39.5 
39 
37.5 
38.5 
38.5 
38.5 
37.5 
38 
Hevea guianensis, Museu Goeldi, Para_. 
Young trees at Cobija, Bolivia _. 
f 31 
28.5 
30 
28.5 
29 
31.5 
I 31.5 
[ 48.5 
49 
50 
48 
N 46 
45 
» 
49.5 
45.5 
47.5 
47 
I 47 
BARK CHARACTERS 
Of all the characters which may be easily observed, those of the 
bark alone offer any aid in distinguishing varieties, and these un- 
fortunately do not admit of measurement. To be sure, the number 
of rings of latex vessels may be counted, but these vary so greatly 
among trees of the same type as to give only very general indica- 
tions. The principal differences are in the relative numbers of stone 
cells and in the color of the bark. 
The vermelha type seems not to differ greatly from the branca 
in the number of stone cells, but the preta type is remarkable for 
the small number of these cells, which causes the bark to be very 
soft in comparison with that of the other types. It is well known 
that cutting the bark induces the formation of stone cells on and 
near the cuts, and this greatly complicates observations. Most of 
the trees in the estradas have been heavily tapped as high as one 
can reach, and samples of virgin bark are hard to secure. To ex- 
amine large numbers of virgin trees, which must be hunted out in 
the jungle, means weeks of search. 
It is very difficult to classify the trees in a given area according 
to bark types. Table 14 shows an attempt at classification in an 
estrada at Kilometer 10, Cobija, Bolivia. The trees classed as 
vermelha have a rose-red bark; those called preta have the charac- 
teristic bark, which is a very dark red, sometimes almost black, 
also very soft. There are other bark colors which do not belong to 
either of these types, and an attempt has been made to classify these 
as tan or light tan as the nearest colors. A Ridgway color guide would 
have been very useful in determining the exact color of each. 
