THE HEVEA RUBBER TREE IN THE AMAZON VALLEY 21 
meters. Yields of 60 trees gave an average of 86.4 cubic centimeters. 
All three of these estradas gave yields which would be considered 
good in plantation trees. 
The seringueiro who tapped the estrada on which Table 1 is based 
says he collects 1,000 kilos in six months. At Tres Casas, on the 
Madeira River, collectors were said to obtain about 600 kilos in a 
season. 
At Calama, on the Madeira River, it was reported that the men 
on the Rio Machado collected 16 to 18 kilos a day. Allowing only 
20 days a month for six months, this would give a production of 
about 2,000 kilos, which is almost certainly too high an estimate for 
Hevea rubber, though not for one man's production of caucho. 
The Guapore Rubber Co., at Guajara Mirim, Matto Grosso, gave 
1,000 kilos as the average production of a seringueiro for five months. 
At Sena, Bolivia, on the Rio Madre de Dios, the average for a large 
number of estradas is 633 kilos, and in the Acre Territory of Brazil 
800 kilos is an average, though 2,000 kilos have frequently been 
obtained from virgin estradas. At Porvenir, Bolivia, the average is 
800 kilos. 
Lecointe (25) estimates the average production of a seringueiro 
at 450 to 500 kilos of fine hard Para rubber and 90 to 100 kSos of 
sernamby. Akers (1, 2) gives an average of 5 pounds a tree for the 
whole Ainazon region, which, assuming that a seringueiro works 
three estradas of 150 trees each, would give 1,000 kilos for each man 
or 680 kilos if only two estradas are tapped by each man. 
From the data in Tables 1 and 2 and also that from the estrada at 
Kilometer 10 near Cobija, Bolivia, it appears that the yields secured 
on estradas visited by the writer are considerably less than Akers 
estimates, which was an average of 3 pounds a tree for the lower 
Amazon and as much as 8 pounds a tree for some other regions. 
AGE OF THE TREES 
There is no doubt that the large rubber trees in South America 
are of great age. In some places there are trees which have been 
tapped for more than 50 years and must have been of considerable 
age before tapping was begun. (Figs. 7 and 8.) In addition to such 
data we have the evidence from annual rings of growth. These are 
formed by the unequal rate of growth at the beginning and at the end 
of the growing season. In the early spring rapid growth takes 
place and wood elements of large diameter are formed; toward fall 
growth slackens greatly and small elements are formed. The alter- 
nate zones of large elements and small elements are apparent to the 
eye in the cross section of a tree trunk as rings, commonly called 
annual rings. 
In tropical climates having uniform growing conditions annual 
rings are usually lacking. In Sumatra, for example, it was prac- 
tically impossible to distinguish annual rings in the rubber trees. 
In regions having alternating wet and dry seasons annual rings are 
formed. However, if a second dry season occurs a second ring may 
be formed the same year. A drought also may cause the develop- 
ment of a second ring in temperate climates. But, in spite of these 
vagaries, the number of annual rings normally corresponds closely 
with the number of years of growth. 
