THE HEVEA RUBBEB TREE IN THE AMAZON VALLEY 
23 
The counts made at Porvenir, Bolivia, and at Kilometer 10 (near 
Porvenir) are shown in Table 3. These trees have an average age 
of 91.8 years and an average circumference of 130.8 centimeters. 
Fig. 8.— A very old tree at Diamantino, on the Madeira River. The exeresences caused by tapping 
have formed ridges. The ridges have been retapped until the whole lower trunk has become 
fluted 
This gives an average diameter increase of 4.53 millimeters per 
annum. Two old trees at Kilometer 10 were too large for the incre- 
ment borer to reach their hearts, but cores 25 centimeters long were 
