DISTRIBUTION OF TRIBES. 437 
undivided, but with the different termination pointed out by 
various synantherologists and insisted on by Delpino. The genera 
may be distributed into two groups. In the first, the Ives, the 
capitula are heterogamous, as in Melampodines, with female 
florets in the circumference and sterile antheriferous ones in the 
disk. In Jva itself, with seven or eight Northern or Central 
American species, the corollas of the female florets are much re- 
duced ; in the two species of Cyclachena and in the monotypic 
genera Euphrosyne, Dicoria, and Oxytenia, all Mexican or Califor- 
nian, the female corollas entirely disappear, the style proceeding 
from the summit of the naked ovary, or at most surrounded by a 
rudimentary ring. In the second group the capitula are strictly 
moneecious, the males usually placed in a different part of the 
plant from the females. The female florets are again apetalous ; 
but each one is completely enclosed in an involucral bract conso- 
lidated with more or less of the outer ones in a close utricle, from 
the beaked apex of which issues the style. These female capitula 
are sometimes one-flowered and distinct; sometimes there are two 
to four female flowers, each in a separate beaked and closed divi- 
sion of acommon mass. Whether this mass is an aggregate of 
two to four consolidated one-flowered capitula or a single capitu- 
lum with the inner involucral bracts closed round the achenes, 
as in Sclerocarpus or Melampodium, and connate with each other 
as well as with the outer bracts, is a disputed point, the advocates 
of each side of the question being certain that they are right. To 
me it appears that the inflorescence may be explained either way, 
the florets not being numerous enough to supply any such 
proof as we have in the case of Albertinia. The four genera 
of this second group are all American, or, at least, as it would 
appear, of American and probably western origin. Hymenoclea, 
two species, is Mexican or Californian ; Franseria, ten species, 
ranges from Chili to California, extending also eastward in 
North America; Ambrosia, twelve species, belongs to the same 
regions, but one or two of its species are also spread over a 
great part of the Old World, as in the above-mentioned cases of 
Elephantopus &c. Xanthium has two or three species, but too 
well known over almost all warm or temperate regions of the 
globe. The genus is probably of American origin, although the 
common species X. strumarium had evidently made its way into 
the Old World long before the discovery of America, and has 
established both in Asia and Europe many so-called species, none 
