the rating of Grade III (fair) based on the system used 
at the National Bureau of Standards for grading wild 
rubber.’” (or details of this system, reference is made 
to Rubber Age 62 (1947) 173). Further notes in the 
analysis are: ‘‘Shrinkage on washing and drying 13.5%. 
Mooney viscosity 17.5. Resins (acetone extract) 17.1% : 
rubber hydrocarbon 80.4% ; insoluble materials 2%.” 
The sample, after vulcanization for 45 minutes (optimum 
cure) at 141°C according to the ACS II test formula, 
had the following tensile physical characteristics: ulti- 
mate elongation 685% ; tensile strength 1885. The elon- 
gation at 200 psi was 251%. 
Hevea rigidifolia (Spruce ev Benth.) Mueller- 
Argoviensis in Linnaea 84 (1865) 203. 
Brazit: Estado do Amazonas, Rio Uaupés, Taracua. Caatinga. Feb- 
ruary 3-6, 1948, Richard Evans Schultes 9673, 9678, 96SO. 
The rubber from Hevea rigidifolia has the reputation 
of being of a very poor quality. Indeed, a rapid exami- 
nation in the field can convince the investigator of the 
soundness of this reputation. here seems, however, to 
be something more complex than would appear on super- 
ficial examination. This is brought out by the unexpected 
results of Mr. McMullan’s analysis of an air-dried sample 
of rubber which I obtained by tapping twenty-six trees 
of Hevea rigidifolia in the extensive caatinga behind the 
settlement of Taracud on the Rio Uaupés, near the 
mouth of the Rio Tikié. The collections cited above are 
from three of the individuals which were tapped. Mr. 
MecMullan’s analysis follows: ‘‘Resin (acetone extract) 
3.369% ; Rubber hydrocarbon (benzene extract) 95.01% ; 
Insolubles 1.68%. Appeared to be somewhat stronger 
and harder than gwanensis.”” 
Brazit: Estado do Amazonas, Rio Uaupés, Ipanoré. Caatinga. 
February 2, 1948, Richard Evans Schultes & Francisco Lopez 9665. 
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