Gardens at Kew in 1947. This study led to the discovery 
that Hevea microphylla and HZ. minor are wholly distinct 
and unrelated concepts (cf. Bot. Mus. Leafl. Harvard 
Univ. 13 (1947) 1-9). Following my trip to Kew, I spent 
nearly a year in the Rio Negro basin of Brazil and Co- 
lombia investigating, amongst other problems, the dif- 
ferentiation of these two concepts. Material was exam- 
ined and collected from the type localities, and this was 
compared with abundant material from other regions. 
This field research fully corroborated the conclusions 
drawn from the previous study of herbarium material. 
During my stay in the Rio Negro area, it was possible 
to see many hundreds of trees of Hevea microphylla 
(prior to 1947 known only from the type locality and 
one nearby station) from the middle Rio Negro to its 
headwaters and in a number of its affuents. Our knowl- 
edge of the range of this most distinctive of all species 
of Hevea, hitherto, to all appearances, a highly restricted 
endemic, 1s now much more extensive. 
As stated above, until recently Hevea microphylla has 
been confused with HZ. minor. This has contributed toa 
misunderstanding of its range. Even had this confusion 
not been so firmly established in the literature, the few 
available collections of Hevea microphylla would have 
been rather difficult to interpret from a phytogeograph- 
ical point of view. Furthermore, while sometimes cor- 
rectly located by earlier writers (e.g., Reintgen, P. **Die 
Geographie der Kautschukpflanzen”* (1905) 28), the con- 
cept has often been erroneously attributed in the litera- 
ture to areas, such as the Acre (de Souza Carneiro, A. J. 
‘*Rubber in Brazil’’ (1913) 8), which are far distant from 
where it actually does occur. 
In 1903, two years before Ule’s description of Hevea 
microphylla, H. Jumelle (** Les plantes a caoutchouc et 
a gutta (19038) 123) published a note on a specimen of 
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