frequent in the Orinoco area, which have been erron- 
eously determined. 
In spite of the fact that Hevea rigidifolia may prob- 
ably occur within the boundaries of three different coun- 
tries, | am of the opinion that, with the single exception 
of H. minor Hemsl., it represents the species which is 
most narrowly restricted in range® and possibly one of 
the oldest of the genus. 
It is of interest to note that Hevea rigidifolia is some- 
times found on caatingas at relatively high elevations. 
The F’rées 21401 collection from Serra de Tunuhy was 
made at an altitude of approximately one thousand feet 
above sea level. I have found that in the peculiar habitat 
of the caatinga flora of these open sandstone mesas or 
campinas in the adjacent areas of Colombia, the greater 
the altitude above the forest floor the more intense the 
conditions of and response to xerophytism. Thus, the 
higher one finds the diminutive xerophytic Hevea nitida 
Mart. ex Muell.-Arg. var. towicodendroides (R. E. Schultes 
et Vinton) R. E. Schultes (in Bot. Mus. Leafl. Harvard 
Univ., 13 (1947) 9-11), the more reduced it is in all its 
vegetative parts. It is significant that the specimens in 
Foes 21401, trom a tree growing so high above the jun- 
gle surroundings, shows no special vegetative adaptations 
correlated with increased intensity of heat, radiation, 
drought or other xerophytic conditions. 
According to Senhor Frées, Hevea rigidifolia is found 
on the flat sandstone mesas as well as on the lightly 
forested slopes formed by the talus from the eroded cliffs 
of the hills. The collection F’rées 21401 was made in the 
light ‘‘talus-forest’” of Serra de Tunuhy, the tree grow- 
*The range of Hevea camporum Ducke, the specific status of which 
is now under question by Dr. Adolpho Ducke (in Bol. Téen. Inst. 
Agron. Norte no. 10 (1946) 19), is not known but may be less extensive 
than that of any other. 
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