348 MR. G. BENTHAM ON COMPOSIT X. 
2. Di- and Trimorphism. 
Di- and trimorphism in individual florets is usually connected 
with unisexuality, the female corollas being either more slender 
than the hermaphrodite, or with a more expanded irregular or 
ligulate limb, or those of the outer rows ligulate and of the inner 
rows slender; or they may be reduced to a mere rudiment or entirely 
wanting ; and the pappus may also differ, that of the female florets 
being often reduced from that of the hermaphrodites or entirely 
wanting; but the value of these differences 1s usually no greater 
than as an indication of sexuality. The reduction or alteration of 
the pappus in the female florets, so often taken advantage of as a 
generic distinction, very frequently produces a purely artificial 
separation of a very few or of a single species from a genus other- 
wise natural, and is now generally abandoned by A. Gray and 
others. On the other hand, with regard to dimorphism in the corol- 
las, although the presence or absence of female florets is often not 
even of generic value, the form they assume when present, whether 
tubular like the hermaphrodites but more slender, or ligulate, is 
sometimes of subtribual importance, as in the case of the separa- 
tion of the last four subtribes of Inuloides from the first six, of 
which this is one of the principal characters. In unisexual 
flower-heads the female corollas are always more or less reduced, 
never having the expanded or ligulate limbs so frequently observed 
in heterogamous heads. 
Dimorphism in the flower-heads independent of the sexes is 
very rare in Composite, and, as far as hitherto observed, only of 
specific value. Linnzus had already informed us that in Gerbera 
(Anandria) bellidiastrum the vernal flower-heads are heteroga- 
mous and radiate, and the autumnal ones homogamous and dis- 
coid; and analogous dimorphisms have since been observed in a 
very few scattered species. Delpino has also observed a certain 
degree of dimorphism in the female flower-heads of two species 
of Franseria, which on that account he establishes as two distinct 
genera—a separation in which it is very difficult to concur. 
9. Differences in the Pistil. 
The ovary and ovule, as to their structure, insertion, position, 
and other relations to other parts of the flower, are absolutely 
uniform throughout the order, and afford no clue to generie or 
tribual distinctions. Nor is the style itself more available in the 
case of the female florets, where its sole functions are those de- 
