In reality, little is known about the genus Castilla in 
the Amazon for there is relatively little good material 
in our herbaria. Under Castilla Ulei, moreover, one can 
find material which would appear to represent several 
species. 
Even less is known of the subspecific variations of Cas- 
tilla Ulei. This is due chiefly to the lack of extensive and 
systematic field studies devoted primarily to this tree. 
Furthermore, the general collector is handicapped in 
making comparative studies and collections of Castilla 
Ulei because of the size and habit of the tree. It is my 
belief, after having seen a relatively large number of 
individuals of this species in the Vaupés and Apaporis 
basins of eastern Colombia, that there are many unde- 
scribed subspecific variants in Castilla as is the case in 
Hevea. Old caucheros (rubber workers) who have cut 
Castilla all their lives have distinguishing names for the 
different ‘‘types’’ of trees which produce the so-called 
ecaucho negro of commerce. These ‘‘types’’ probably 
would be found to represent taxonomically distinct sub- 
specific variants, for it is my experience that the cauch- 
eros of eastern Colombia are rather keen in their percep- 
tion of differences in plants. These subspecific variants of 
Castilla Ulei cannot be fully understood, however, until 
some investigator carries out field studies on thousands 
of individuals over a rather wide area. 
The form described here, lecithogalacta, is one of the 
most common and widely recognized of the ‘‘types’’ of 
caucho negro in the Upper Vaupés River. The very ap- 
propriate name yema de huevo (‘‘egg-yolk’’) refers to the 
bright yellow color of the latex. As the latex, which is 
extremely thick, flows out of the cuts, it is a deep cream ; 
on contact with the air, however, it almost immediately 
deepens in color and very shortly becomes a yellow so 
brilliant that one finds it difficult to realize that one is 
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