20 BULLETIN 1422, U. S. DEPARTMENT OF AGRICULTURE 
or scaffolds in tapping, and they are forbidden by law in Bolivia, 
though they are still occasionally seen there as well as in Brazil. 
At this rate, even allowing a height of 3 meters (and most trees are 
not now tapped so high), the tapping surface would of necessity be 
changed once in the season. The space between rows is 3 or 4 cen- 
timeters in width, and these spaces with the rows of cuts would use 
up practically all the bark on the Matto Grosso trees in one season. 
The Bolivian trees would last somewhat longer, but not more than 
two seasons, after which the trees should be allowed to rest for at 
least two years. In most cases such rest periods have been given, 
and now with thousands of idle estradas even longer periods are 
given for recuperation. Longer intervals are surely needed, for there 
is ample evidence that many trees have been killed by the severity 
of the tapping, and most old trees show evidence of poor bark re- 
newal. Anything like the incessant tapping to which most of the 
trees in the East were formerly subjected would be impossible with 
machadinho tapping. The remarkable way in which these oriental 
trees have endured the strain upon them indicates that it is not loss 
of latex but loss of tissue which has exhausted the South American 
trees. 
NUMBER OF TREES IN AN ESTRADA 
The number of trees in an estrada depends somewhat on their 
distribution in a given area, somewhat on the lay of the land, but 
more particularly on the number of trees which the seringueiro feels 
like tapping. The estrada on which Table 1 is based is an unusually 
large one, containing 265 trees, of which 239 were actually being 
tapped regularly when the data were taken. Usually the number of 
trees tapped is somewhere between 100 and 200. At Sena, Bolivia, 
the average is 150 trees; in the Acre Territory, perhaps a little less. 
Akers (2) estimates the number at 135 to 150 per estrada in the Ma- 
deira region. Lecointe (25) quotes a report on the Rio Tapajos, by 
Raymundo P. Brasil, in which it is estimated that in the municipality 
of Itaituba 287,045 trees were tapped in 5,407 estradas, or 53 trees 
per estrada. This is probably a smaller number of trees per estrada 
than is common in most regions. 
YIELDS OF THE TREES 
Tables 1 and 2 give the yields of latex of a number of Hevea trees, 
each from one day's tapping. The yields of individual trees are 
given for comparison with individual-tree yields in the East and 
elsewhere. Yields from a single tapping are unsatisfactory for such 
purposes but are the best available data, since very few records of 
yields of individual trees in the Amazon region have ever been 
published. 
The maximum yield in Table 1, 536 grams, was the highest 
observed by the writer in the course of his trip in South America. 
Reports of much higher yields are current; trees are even reported 
which yield as much as 4 liters per tapping, but if such yields exist 
they are very rare. 
Another estrada at Kilometer 10, between Cobija and Porvenir, 
Bolivia, showed about the same variations in yield of individual 
trees as the two estradas included in Tables 1 and 2. The highest 
yield was 350 cubic centimeters of latex, the lowest 5 cubic centi- 
