MR. G. BENTHAM—REVISION OF THE GENUS CASSIA. 509 
almost arctic zones at the two extremities of the great Andine range, giving evidence of 
an exceedingly remote common origin and wide extension, of a retention of identical 
characters through countless ages, and a total extinction in the intermediate space, which 
had become no longer so well suited to their unmodified constitution. 
There are two species, C. occidentalis and C. Tora, which I have already mentioned as 
exceedingly abundant in waste and cultivated places all round the tropics, although I 
have classed the sections they belong to, Oncolobium and Prososperma, as essentially 
American. ‘I do so because the fact of all the nearest allies of these species being exclu- 
sively American, the Asiatic and African stations by roadsides in gardens and other culti- 
vated places, and other circumstances already pointed out by Alph. de Candolle (Géo- 
graphie Botanique, 772) in regard to C. occidentalis show the probability of their com- 
paratively recent introduction from America, although not necessarily through human 
agency, and possibly even before the discovery of America by Europeans. There remains 
to be considered whether each of these two species has not a truly Asiatico-African 
representative, the C. Tora having been distinguished by most botanists from C. obtusifolia 
as well as C. Sophera from C. occidentalis, systematically as well as geographically. But 
the straight and curved pod of C. Tora and obtusifolia respectively occur in both hemi- 
spheres (though the straight one may be more common in Asia than in America), and 
sometimes on the same individual at different stages of maturity, or perhaps varying 
according to the degree in which maturity has been hastened or retarded by climatological 
conditions. As to C. Sophera, however, whether it be a distinet species or a variety of 
C. occidentalis, it certainly is much more abundant in Africa and Asia, and especially in 
Australia, than in America ; and though generally said to be growing with C. occidentalis, 
Roxburgh says that one form of it, his Senna purpurea, was raised from seeds received 
“from the mountainous parts of the coast." It may also be observed that it was early 
confounded by Forskohl and others with one of the true Sennas, and seeds may have been 
"sent out to the West Indies with those of C. angustifolia. I have seen specimens from 
various parts of Central America which are probably truly indigenous; but, generally 
speaking, C. occidentalis seems more disposed to pass into C. ligustrina in Central 
America, and into C. Sophera in the Old World. It remains therefore, with me at least, 
still a very doubtful question, 1st, whether C. Sophera is really any more than a compara- 
tively recent and uncertain variety of C. occidentalis, and, 2ndly, whether, if it be really 
a tolerably constant species of older date, it had or had not its origin in the Old World. 
In tropical and subtropical Eastern Australia it appears to have a still more definite 
aspect than in Asia or Africa, to diverge into forms not known elsewhere, and to have 
more the appearance of being indigenous, besides that the typical C. occidentalis has not 
yet been received from thence. The balance of evidence would perhaps lead one to con- 
jecture that Q. Sophera results from some offset of the group of American Oncolobia which 
had found its way into the Old World at a very early period, but yet not long enough 
isolated or not sufficiently modified in character to have lost the power of combining with 
C. occidentalis when brought into its contiguity. 
"If further observation should lead to the conclusion that C. Sophera is really a diver- 
