their small size they are poor producers of latex, and the 
latex itself is of inferior quality. However, they would 
be of scientific value because of their rarity. ”’ 
It would seem from this statement, and from others 
in the same report which indicate that the greater part 
of the upper Rio Negro production of rubber is from 
Hevea Benthamiana, that we are justified in inferring 
that Hevea rigidifola furnishes none of the rubber pro- 
duced in the area. This does not, however, assist in the 
appraisal of the quality of the rubber, for it is clear that 
the principal reason for not utilizing Hevea rigidifola 
would be its small size. It might possibly be true that, 
as in the case of Hevea nitida var. toaicodendroides, its 
latex could be of high quality even though almost un- 
obtainable due to the diminutiveness of the plant. 
The fact that in its native state Hevea rigidifolia is 
of no commercial interest does not, however, indicate 
that it is devoid of importance to the scientific program 
of Hevea-investigation now in progress cooperatively be- 
tween the United States Department of Agriculture and 
several Latin American countries. I consider that one 
of our most urgent tasks is the introduction of extensive 
living material of Hevea rigidifolia from several different 
localities to one or several of our experimental nurseries. 
The differences between Hevea rigidifolia and the spe- 
cies commonly exploited, especially HZ. brasilensis, are 
so great that we would be justified in expecting a num- 
ber of interesting, and perhaps even revolutionizing, 
characteristics to appear as a result of an intensive pro- 
gram of selection and breeding. 
This small tree is native to isolated sterile (cretaceous) 
sandstone caatingas on the pre-cambrian granitic Brazil- 
ian shield where the pH is probably rather highly acidic 
and where conditions of psammophytic and chersophytic 
drought prevail even during the rainy season. How this 
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