Origin and Development of the Composite. 215 
The Homochrominae is the basal sub-tribe and Solidago the 
primitive genus. An examination of any of the ordinary keys to 
the British flora, such as that in Hayward’s Botanist's Pocket Book 
will show how closely allied are the three genera, Senecio, Solidago 
and Inula. The case of the Inulinae is discussed above. The 
imbrication of the involucral bracts and the rigidity of the pappus 
hairs are apparently the best characters which can be found to 
distinguish Solidago from Senecio, and these apply only to the 
British species. The rigidity or silkiness of the pappus varies, 
especially in Senecio, while that same genus has exotic species in 
which the calyculus is so well developed that the involucre must 
be described as imbricate. The type VIII styles of Solidago are 
the real tribal distinguishing feature, but even this distinction 
is not absolute, since various species of Senecio show the type VIII 
and type VII styles. 
The place of origin of the Homochrominae is clearly somewhere 
about the borders of the Mexican and U.S. regions. This sub¬ 
tribe has in all probabililty given the Bellidinae, while the 
Grangemae and Conyzinae have probably come from the 
Heterochrominae (see Chap. X, D), the Conyzinae via Erigeron, 
which passes on the one hand into Aster and on the other into 
Conyza. 
The transition from the Homochrominae to the Heterochrominae 
can be located in the region of origin of the former sub-tribe. The 
chief genera of the latter sub-tribe are Aster, Erigeron, Olearia, 
Felicia and Celniisia ; of these Olearia and Celmisia are restricted 
to the Australian region, while Felicia is almost confined to South 
Africa. The other two genera are more or less cosmopolitan and 
are so very closely allied that the transitional species are com¬ 
paratively numerous and the genera in these cases are distinguished 
only by the so-called indefinable characters of the taxonomist. On 
the other hand Solidago is “ only distinguished technically from 
Aster and its immediate allies by the homochromous florets, the 
ray-florets, when present, being yellow, like the disk—a character 
in general of so little value that it cannot, in Senecio for instance, 
be admitted as of more than specific importance ” (Bentham, 1, 7). 
1'he Baccharidinae, which include only the large genus 
Baccharis and two very small genera, show affinities with the 
Heterochrominae and especially with the Conyzinae in styles and 
stamens (see Fig. 7), corolla-form, pappus, involucre, receptacle 
and phyllotaxis. The chief distinctions are the dioecious capitula 
