by representative of the genus found on the sterile tops 
of sandstone mountains in the Caqueta and Vaupés. It 
yields a rubber which is described by chemists as ‘‘very 
good,’ an exceedingly interesting report in view of the 
inferior and worthless quality of the rubber of Hevea 
viridis itself. Unfortunately, due to its diminutive size, 
Hevea viridis var. toxicodendroides is commercially with- 
out value because it cannot be tapped. Nevertheless, it 
represents a very interesting variety which might be of 
use in a breeding program. It has no common name 
which has come to my attention. 
Ill. 
The distribution of Hevea in Colombia can best be 
understood if it be presented according to river-systems. 
VauprEs River Basin: The I[tilla and the Vaupés it- 
self above the falls of Yurupari are populated by an abun- 
dance of Hevea guianensis var. lutea, considerable H. 
guianensis and a relatively small amount of H. Bentham- 
lana; H. viridis is apparently entirely absent. Below 
Yurupari, the Vaupés is very rocky, interrupted by in- 
numerable rapids and one finds proportionately less 
Hevea guianensis var. lutea, little H. guianensis but 
much more Hi. Benthamiana; H. viridis is extremely 
abundant in igap6s near rock outcrops; H. viridis var. 
toxicodendroides is found on sandstone mesas at Yapo- 
boda near the headwaters of the affluent Cuduyari and 
on Cerro Cireasia; HZ. rigidifolia may occur below Mitt 
near the Brazilian border. 
Apvaporis River Basin: In the upper and middle 
basins above the falls of Jerijerimo (which correspond to 
Yurupari geologically and geographically), the most 
abundant trees are Hevea guianensis var. lutea and H. 
guianensis; H. Benthamiana (including several unusual 
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