YIELD AND DENSITY OF LATEX 79 



the number of collectors employed and the average 

 number of trees allotted to each collector. The ship- 

 ments from these districts in the season 1912-13 

 amounted to 21,000,000 pounds, and to obtain this crop 

 27,000 tappers were necessary, each working an estrada 

 containing on an average about 150 trees, for a period 

 of 1 60 days extending over seven months, from June to 

 January. Investigations conducted on about 100 prop- 

 erties revealed the fact that the monthly deliveries of 

 rubber from each collector averaged no to 112 pounds, 

 or 770 pounds, slightly more or less, during the season ; 

 this equals a total output of 20,790,000 pounds from 

 some 4,050,000 trees, or an average yield of 5*13 pounds 

 per tree. 



In the third section of the Amazon Valley, comprising 

 the rubber-producing districts of Bolivia, the Acre terri- 

 tories, the Upper Purus and Jurua, the Jutahy, Javary, 

 and other rivers, a higher average yield is obtained. 

 This is due to the fact that the majority of the trees 

 have been worked for a comparatively short period, and 

 also because a large number of virgin trees are brought 

 into tapping annually. In Bolivia the output for the 

 season 1912-13 was 6,700,000 pounds, and this quantity 

 was produced by 7,500 collectors from 1,100,000 trees, 

 equivalent to a return of a little less than 6 pounds 

 per tree. In the other districts enumerated the aggre- 

 gate crop was 25,900,000 pounds, gathered by 26,000 

 collectors from 3,770,000 trees, an average of 6'8 pounds 

 per tree. In these calculations all reference to caucho 

 (castilloa) is omitted, no data of any kind being avail- 

 able at present for working out the average per tree, on 

 account of the methods employed for the collection of 



