with Mocoa in the eastern lowlands. The third, and 
shortest trail, connecting the Valley with the Rio Juan- 
ambu drainage to the north, is probably little changed 
from 1801 when Humboldt and Bonpland traversed it 
twice, or from 1541 when Hernan Pérez de Quesada 
fled homeward along it from his wretched search for 
El Dorado. 
During the long period of relative isolation, a great 
variety of curious cultivated plants were brought into 
the Valley. Some are of scant importance today and may 
never have enjoyed a wide appreciation among the Val- 
ley’s inhabitants. Others, the predominant food, medi- 
cinal and narcotic plants, have come to assume very great 
importance in the economic and social life of the natives. 
Certain plants, known nowhere else, have evolved in the 
Valley under the influences of cultivation. Such has 
come to pass with the tree Datura drugs. 
The genus Datura consists of eight to twelve herba- 
ceous species (2, 8, 28), with their centre of diversity 
in Mexico and southwestern United States: and three 
or more (7) to fourteen (28) arborescent species centered 
in the northern Andes. In the absence of a modern and 
comprehensive revision of the genus, Safford’s account 
of 1921 has been widely accepted. However, were we to 
continue employing his species concept today, the diver- 
sity of herbarium material available now would allow us 
to define thirty or more ‘‘species’’ of tree Daturas (sect. 
Brugmansia) alone. Recently, I have pointed out that 
almost all tree Daturas belong to one of three species 
and that the few remaining plants are probably hybrid 
or aberrant individuals (7). The variability expressed in 
the tree Daturas as a group has been enhanced through 
their cultivation by many native peoples; in fact, their 
absence from any natural vegetation implies that their 
recent evolution has taken place entirely under man’s 
influences. 
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