ing in gravel and among huge, scattered blocks under 
severe conditions of chersophytic drought. Senhor Fr6ées 
described the habitat to me as follows: ‘‘Hevea rigidi- 
folia in this locality (Serra de Tunuhy) is fair-sized be- 
cause it is under a light forest; the crown of the slender 
Hevea protrudes above the forest seeking light. ... I 
estimate that the mesa-like top of Tunuhy is 1000 feet 
above the forest floor, but I ascended only about 600 
feet, where I collected number 21407.”’ 
Variability of Hevea rigidifolia 
The present study of the variability of important spe- 
cific characters of Hevea rigidifolia is based upon an ex- 
amination of: (1) the type and a duplicate type in the 
Royal Botanic Gardens at Kew; (2) a photograph of a 
specimen of the type collection from the Delessert Her- 
barium; (8) one duplicate type preserved in each of the 
following institutions: Gray Herbarium of Harvard 
University ; the New York Botanical Garden; the Brit- 
ish Museum of Natural History; the Fielding Herbarium 
at Oxford University; the Herbarium at Cambridge 
University, and the Herbarium Amazonicum Musei 
Paraensis (Museu Goeldi) in Belém do Para; (4) thirty- 
six specimens of the four Frées collections; (5) a young 
individual introduced to cultivation at the Instituto 
Agronomico do Norte by Baldwin in 1944. Further- 
more, [ have also had the opportunity of questioning 
Senhor Fr6es in great detail about the habit and habitat 
of the trees from which his collections were made. 
It is clearly apparent from a study of these collections 
from five different localities that Hevea rigidifolia is an 
exceptionally stable species. It is indeed unusual to find 
a concept of such stability in this very variable genus. 
Unless later investigations with large quantities of seed 
[ 111 ] 
