species will react in growth as well as in quality and yield 
of latex when planted on a rich soil with an abundant 
availability of water is certain to be enlightening.” Selec- 
tion should be carried out to some extent in the caatingas 
in order to secure for scientific study the most outstand- 
ing individuals from several points of view. A still more 
rigorous and accurate selection can be practiced in nurse- 
ries if large numbers of seedlings are planted and studied 
under controlled conditions. The potentialities of this 
species as a fast grower, outstanding yielder, disease- 
resistant strain, drought-resistant material, root-stock, 
crown-budding stock, as well as in numerous other re- 
spects, are certainly worth investigation. 
The very fact that Hevea rigidifolia is one of the most 
distinct of the dozen or more species of the genus is in- 
dicative of the value which it might have in a plant- 
breeding program. This is especially true when one con- 
siders the possibilities which might arise as a result of 
chromosome incompatibility. 
It is likewise imperative that we collect ample speci- 
mens of the coagulated latex from Hevea rigidifolia in 
its native state for chemical examination and later chem- 
ical comparison with latex from the same species culti- 
rated under varying ecological conditions. It is possible 
that, as in the case of Hevea nitida in the igapés of the 
Vaupés of Colombia, of AZ. Spruceana and of H. pauci- 
Jlora var. coriacea, the rubber of Hevea rigidifolia, of 
itself, will be of little or no commercial value. The rapid 
progress in the study of the synthetic elastomers, how- 
ever, is creating a demand for rubbers of varying proper- 
ties for use as ‘‘fillers’’ and the latex of no species of 
Hevea should be overlooked as a potential raw material 
for utilization in the synthetic rubber industry. 
"The individual introduced by Baldwin in 1944 to Belém do Para, 
planted on very light white sandy soil, exhibits an unusually slow 
growth. It is, at three years, only about five feet tall. 
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