in thickness. ‘They may dehisce as in some specimens of 
Hevea Spruceana where the explosion is less violent than 
in most other species, but the structure of the valves in- 
dicates definitely that dehiscence is explosive. The ‘‘half- 
opened fruit’? drawn by Hemsley’s artist and actually 
preserved in that state on the herbarium sheet is due, I 
believe, to the fact that, as shown by the whiteness of 
the seeds, the capsule was not quite mature and that the 
artificial heat applied in making the dried specimen 
caused it to open partially while still under pressure in 
the plant press. This has often occurred when I have 
been drying Hevea specimens by means of artificial heat. 
Unless we can find some definite evidence of slow open- 
ing and gentle dropping of the seed in Hevea minor, we 
are making an unsound assumption in believing that such 
a mode of dehiscence is normal. 
In Hevea microphylla, however, there is indeed very 
strong evidence that slow dehiscence is the rule, for the 
entire structure of the valves is distinct and is such that 
a violent opening and shedding of the seeds would be 
mechanically impossible. The valves are provided with 
an excessively thin—0.3 mm.—endocarp which is coria- 
ceous, not even woody. Clearly, this structure is too 
weak to build up the tension necessary for a violent 
bursting. The valves open slowly, as Ducke has pointed 
out, and let the seeds drop slowly to the ground, per- 
sisting for some time on the peduncle (as often is the case 
in Hevea Spruceana) and then, when the seed is shed, 
twist themselves rather tightly due to their almost papery 
consistence. ‘This is indeed unusual in the genus. 
There would appear to be a strong ecological differ- 
entiation between Hevea minor and H. microphylla. The 
former is known only from the dry, sandy scrub-forest 
or caatinga of the Casiquiare. The latter, so far as avail- 
able collections indicate, inhabits forests which are peri- 
[7] 
