tioned maintain that Micrandra latex cannot be mixed with that 
of the rubber-yielding species of Hevea, the acid-coagulation of 
which it prevents. This unexpected effect is brought about like- 
wise if the latex of Hevea nitida Mart. ex Muell-Arg. be added 
to that of species, such as H. guianensis Aubl., which furnish 
good rubber (Schultes, R. E.: “The genus Hevea in Colombia” in 
Bot. Mus. Leafl., Harvard Univ. 12 (1945) 11; Seibert, R. J.: “A 
study of Hevea (with its economic aspects) in the Republic of 
Peru” in Ann. Mo. Bot. Gard. 34 (1947) 268). 
In quantity (and perhaps also in quality of rubber), latex 
varies from tree to tree, but we do not yet have precise data on 
this phenomenon, as we do for some species of Hevea. Micran- 
dra minor, growing along or very near water courses, yields 
much more latex than does M. siphonioides, an inhabitant of 
higher, well drained sandy savannahs situated well back from 
streams. The latex of the former species is thinner and freer 
flowing than that of the latter. For this reason, we might justifia- 
bly assume that, if Micrandra has ever been commercially ex- 
ploited, it was M. minor which was cut usually in preference to 
M. siphonioides, especially so since it is a much more abundant 
tree and much more accessible by canoe along the river banks. 
Little indeed is known about the rubber from Micrandra. 
According to Spruce, Micrandra yields “pure rubber.” Ule, like- 
wise, stated that Micrandra rubber is of good quality. Allen’s 
visual evaluation of the rubber of M. minor and M. siphonioides 
likewise suggests that it is of good quality. 
There is very little chemical information available on this 
rubber. Mr. A. V. McMullan of the United States Department 
of Agriculture reported (letter to R. E. Schultes, June 16, 1949) 
the following data after studying an air-dried specimen of rubber 
from Micrandra minor (Schultes et Murca Pires 9075a): “Resins 
(acetone extract) 3.78%; rubber hydrocarbon (benzene extract) 
87.08%; insolubles 9.14%. Appeared to be somewhat softer and 
weaker than brasiliensis. This sample very difficult to enter solu- 
tion which may indicate a high polymer rubber. Merits more 
study.” Rubber from the leaves and bark of two trees of M. 
Lopezii were examined—Schultes et Lopez 9638: (bark) Resins 
5.40%, rubber hydrocarbons 2.06%, “excellent rubber, clear, 
strong and elastic”; (leaves) resins 13.93%, rubber hydrocarbons 
100 
