way closely allied. I published the results of my studies, indic- 
ating that H. microphylla is, indeed, the most unique species in 
the genus and that, in addition to morphological characters 
easily to separate it from all other species, there are. likewise, 
strong ecological differences setting H. microphylla apart from 
H. minor: periodically and deeply flooded forested river banks 
in the former: scrub-forest in sandy, almost permanently 
flooded caatingas in the latter. Seibert accepted my treatment 
of H. microphylla as distinct: and, in 1949, Ducke (in litt.) 
likewise followed my interpretation, although, in publishing his 
acceptance of it in 1950, he stated that it was ‘‘lamentable. 
because it would have been better, for true scientific purpose, if 
that change could have been avoided.”’ 
For several years following my article in 1947, I was able to 
carry out intensive plant exploration in the Rio Negro basin of 
Brazil, Colombia and Venezuela, studying abundant stands of 
Hevea microphylla. These studies substantiated the unique- 
ness of this species and led, in 1952. toa paper on its range and 
variability and an extended description of the concept. At that 
time, I wrote: There are so many differentiating characters of 
the first magnitude to be found exclusively in H. microphylla 
that we are forced to regard the concept as standing entirely 
alone with no close allies in the genus’’. In 1967, whilst on the 
Alpha-Helix Amazon Expedition, I was fortunate again to 
meet with extensive stands of H. microphylla, not too distant 
from the type locality. These studies intensified my belief that 
we were concerned here with a species that had gone off on an 
evolutionary tangent of its own and that it, therefore, merited 
some special recognition in any treatment of infrageneric clas- 
sifications of the genus. 
II]. THE UNIQUENESS OF HEVEA MICROPHYLLA 
Hevea microphylla stands quite alone in the genus. It is 
unique in several basic characters — characters in both the 
flower and fruit and which are so distinct that there appear to be 
no intermediates. 
The pistillate flowers of Hevea microphylla differ markedly 
from those of all other species in having a greatly swollen torus 
250 
