Origin and Development of the Composite. ‘2*25 
insolation of the North American as compared with that of the 
Andine region, or possibly as the result of a mutation similar to 
that which produced the red sunflower. The result of these and 
other slighter changes was the origin of Aster from the Solidago 
type. 
Oligocene Period. 
While these events were occurring in the Mediterranean and 
North American regions, the ancestral home of Senecio was becoming 
rather crowded by its numerous progeny. The accompanying 
spread of the genus led, during the lower Oligocene, to another 
invasion of the caatiugas among the Andine foothills near the 
sources of the Amazons. These regions were wooded hut the 
altitude and soil conditions combined to produce well lighted, sunny 
woods with comparatively small trees, rather than the dense, 
umbrageous type of forest characteristic of the lower parts of the 
Amazons valley. Such conditions favoured the development of the 
herbaceous perennial type of Senecio , and as the tendency to 
economy in polliniferous tissue became effective tails were devel¬ 
oped to the anthers. This economy was counter-balanced by an 
extravagance in the development of a bifid upper lip in the ray florets. 
These two changes, the former an example of orthogenesis, the 
latter an example of a mutation which can scarcely he called 
orthogenetic, together with some very slight changes which did 
not involve any change in general habit, resulted in the production 
of Trixis. 
This habitat, it will be remembered, is that of the scandent 
Lobelioid ancestors of the Composite. It is not surprising, there¬ 
fore, to find that these invaders from the mountains, both Senecio 
and Trixis , developed scandent forms. In the former the flower 
remained typical of the genus at least until the end of the Oligocene. 
In the latter, which was a comparatively new form not at that time 
quite stabilised, floral changes accompanied the change in habit. 
The barbellae of the pappus setae elongated to give a plumose type 
and the anther tails became somewhat longer ; at the same time 
the supply of extra material for the inner lip of the corolla was cut 
down by the innate economy of the family. These changes, all of 
which are expressions of general orthogenetic tendencies in the 
family, together with slight anthocyan changes in the corolla, 
combined to originate the genus Mutisia during the middle 
Oligocene. 
