438 MR. G. BENTHAM ON COMPOSITE. 
of which, however, appears to have acquired much of a local cha- 
racter, and some are repeated in America. X. macrocarpum, DC., 
first described as a Mediterranean plant, is believed to be a more 
modern introduction from America; X. spinosum, Linn., which 
has quite recently extended its range over new countries (e. g. 
Australia), was originally said to be Chilian. 
5. PETROBIEX form a small subtribe of three genera compri- 
sing 4 species, very distinct, by their strictly dicecious capitula, 
and remarkable for the flowers of the two sexes being more 
nearly similar than in most heterogamous Composite. The co- 
rollas of both sexes are regular, though still different in propor- 
tions ; the stamens in the females are more developed than usual, 
having well-formed anthers, although small, free, and without 
pollen; the styles of the males are undivided in one genus, 
branched in the two others. They are trees or shrubs, with the 
other characters of Helianthoidew. Geographically they are all 
of limited range. Podanthus, with two species (or varieties ?), is 
Chilian; Astemma, a single species as yet only known from Hum- 
boldt’s original specimen with female capitula, is from the Andes 
of Quito; the third, Petrobium, also monotypic, is insular, being 
limited to the island of St. Helena. Several of the above circum- 
stances suggest the probability of these genera exhibiting the 
nearest approach to the primitive form of Composite. 
6. ZINNIEZ are a group of five or six genera, comprising twenty- 
five species, only separated from the great mass of Verbesinew by 
the ligulate corollas of the female florets sessile or nearly so, and 
persistent on the ripe achene, without any external pappus or 
border at the base, and so deceptively continuous with the achene 
as in some instances to have given rise to a query whether this 
corolla did not really stand in the place of the pappus and represent 
the calyx-limb—a query, however, to which a careful examination 
will at once give a negative answer. These genera are all West- 
Ameriean and chiefly of the Mexican region ; Tragoceros four 
species, Zinnia twelve species, Sanvitalia three or four species, 
and Aganippea two species limited to that region; Heliopsis has 
three species, of which one extends southwards along the Andes 
and the two others eastwards in North Ameriea. One or two 
species of Zinnia, long in cultivation for ornament, have established 
themselves as colonists in some parts of the Old World. Phil- 
actis, a single species, also Mexican, is unknown to me, but pro- 
bably belongs to the Zinnia group. 
