the floodable areas. In the Caraparana and Igaraparand, 
formerly the centres of the famous and powerful Casa 
Arana which exploited rubber with Indian labor forced 
by torture and death, Hevea guianensis and H. guian- 
ensis var. lutea predominate. Only a small amount of 
Hevea Benthamiana is found along the lower reaches of 
the Igaraparana and in the vicinity of the Quebrada 
Menaje. Nothing is known about the distribution of the 
little understood species Hevea Fowu and H. glabrescens 
of this basin. I did not find Hevea viridis in the Putu- 
mayo drainage area, but Ducke reports one collection of 
this species from Occidente on the Rio Putumayo. 
AMAZON RIVER Basin: Colombia has only avery short 
stretch of the Amazon, the southern limit of the wedge- 
shaped ‘‘trapecio amazonico.’’ Nevertheless, this short 
stretch, receiving several small rivers or large creeks (the 
Loretoyacu, Hamacayacu, etc.) is of special importance 
in a study of Hevea. This small area is the only part of 
Colombia where Hevea brasiliensis occurs. As yet, we 
do not know exactly how far into the ‘“‘trapecio’’ this 
species penetrates, but it probably reaches only to the 
headwaters of the creeks which empty directly into the 
Amazon above Leticia. In this area, however, Hevea 
brasiliensis var. subconcolor predominates, occurring in 
swampy habitats to the exclusion of other species. There 
are several very distinct forms of the variety in the Leti- 
cia area. On the few higher knolls, Hevea guianensis is 
represented. 
IV. 
The following key has been prepared with the needs 
of the field man in mind. A number of the characters— 
position of the leaflets, color of the latex, consistency and 
color of the bark, etc.—are rather easily observed in the 
field even though they may not be available to the stu- 
[ 15 | 
