may, and most probably will, be made in the future, be- 
fore presenting a general and admittedly provisional out- 
line of the problem. 
For three and a half years,’ | have been engaged in 
botanical work on the Amazonian watershed of Colom- 
bia. This work has been carried out principally along the 
following rivers: Vaupés, Itilla, Ajaju, Macaya, Apap- 
oris, Cananari, Piraparana, Caqueta, Miritiparana, Put- 
umayo, Loretoyacu, Hamacayacu and Boiauasst, and in 
the Leticia area of the ‘‘trapecio amazonico.”” In addi- 
tion to my own observations and collections, | have had 
data kindly made available to me by Hans G. Sorenson 
of the Office of Rubber Plant Investigations of the 
United States Department of Agriculture and Paul H. 
Allen of the Rubber Development Corporation. I have 
also had the benefit of numerous conferences with Dr. 
Adolpho Ducke whose knowledge of Hevea in Brazil is 
extensive and profound. From these sources, it has been 
possible to reconstruct the distribution of the genus in 
Colombia according to river systems. It should be borne 
in mind that the range of Hevea in Colombia covers a 
vast area, extraordinarily difficult for travel and rather 
varied as to topography. We have observations from 
only a few localities in this great drainage-area and ade- 
quate herbarium material from still fewer localities. 
It is evident that there remains much to do before we 
‘an understand fully the details of the specific distribu- 
tion of Hevea in Colombia. Only a beginning has been 
made. Fortunately, however, this beginning has been 
well extended over a wide area so that we have, geo- 
graphically speaking, a relatively complete representa- 
7 1941-42: National Research Fellow in Botany; 1942-43: Field 
Technician, Rubber Development Corporation; 1943 to the present: 
Associate Agronomist, Rubber Plant Investigations, United States 
Department of Agriculture. 
