YALUE OF CHARACTERS. 847 
to a corolla with a rudimentary or small abortive ovary without 
style or stamens, and therefore called neuter) has been considered 
by many synantherologists an absolute generic indication; and 
although now generally abandoned in the case of the enlarged 
neutral florets of some Cynaroidee, it has been strictly adhered to 
by Lessing, De Candolle, and others in the case of Asteroidee, 
Helianthoidew, and others with radiate flower-heads. But in 
many genera it appears to establish a purely artificial distinction ; 
it separates from large and natural genera a few species or a 
single one without any other peculiarity but what every one 
admits is purely specifie; and besides it is in these cases not 
always strictly constant. I would therefore, with Schultz Bipon- 
tinus, reunite Galatella with Aster, Delucia with Bidens, Leptosyne 
and others with Coreopsis. In some Helianthoidez, however, it 
prevails through so large a number of species, otherwise evidently 
congeners, that I have adopted it among the essential generic 
characters of Helianthus, Viguiera, Tithonia, Oyedea, Gymnolomia, 
Rudbeckia, £c.—and even as the sole generic distinction between 
Aspilia and Wedelia, Actinomeris and Verbesina—but more as a 
matter of convenience than of conformity to nature, in large 
groups of species where no better principle of subdivision has yet 
been proposed. This sterility of the ray-florets is yet more con- 
stant in the majority of the genera of the tribe Arctotidez, though 
here, again, there are a few, such as Arctotis itself, where they are 
fertile. 
Unisexuality of flower-heads is sometimes a constant generic or 
subtribual character; the heads are, for instance, constantly 
moncecious in Ambrosiew, constantly dicecious in Petrobiex, 
Tarchonanthese, Baccharis, Lycoseris, Moquinia, &c. In these 
cases the male heads always consist of hermaphrodite sterile 
florets, with the anthers perfect, the style always present, but the 
ovary abortive and usually reduced to a mere rudiment; in the 
female heads the pistil is perfect, the anthers often present, but 
free and without pollen, or reduced to small rudiments or entirely 
deficient. In several Inuloidez (Plucheines or Gnaphalies) the 
unisexuality of the flower-heads is less perfect and more incon- 
stant, the male heads having occasionally a few female fertile 
florets in the circumference, the females one, two, or more her- 
maphrodite and sterile ones in the centre, and the proportions 
varying sometimes from species to species or from individual to 
individual. 
