25 
Origin and Development of the C oviposit ce. 
principle thus :— “ That differentiation and decrease of range go 
together is a principle that seems to prevail throngh the whole 
plant world ” (IX, 22,p.314). 
Age and Area. The most striking example of the action of the 
law of Age and Area is the world-wide distribution and numerous 
centres of concentration of the basal genus Senecio. No genus in 
the family has a distribution at all approaching that of Senecio , 
except Gnaphalium , the basal genus of the Inuleae-Cynareae branch, 
which is of comparatively ancient origin. Along this line we can 
follow the genus Gnaphalium in its period of full vigour and the 
gradually higher physiological differentiation and restriction in 
area which culminates in the Buphthalminae; then from this 
“ apparently expiring race ” we have the vigorous “ young 
progressive race ” starting into new life in the Cynareae with all the 
characteristics given by Bentham (see above Sect. A). The 
significance of these small groups, such as the Buphthalminae and 
Liabinae, which give much larger and more widely spread groups 
will be made clearer in the following chapter, Sect. C. 
The wide distribution of some genera of the Heterochrominae, 
and Verbesininae also illustrate the principle of Age and Area. Other 
examples are Liabum, the Enpatorium-Mikania plexus, Vernonia, 
Trixis and Ursinia ; in fact the primitive genus in almost every 
sub-tribe and the primitive sub-tribe in almost every tribe, in 
addition to the primitive genus of the whole family show the 
greatest area occupied by the oldest member of the group. There 
are exceptions such as the Buphthalminae and Nassauviinae, but 
these are peculiar groups, and their rejuvenescence to give larger, 
wider spread, more prolific races is in accordance with the general 
life history of a race as given by Bentham. 
One point, however, requires consideration. Bentham regards 
these “decaying races” as ancient, but the facts of the individual 
cases show that they are more probably derivative races, arising 
comparatively recently from the widespread vigorous races. In 
Bergson’s phraseology they are the last, small reverberations of the 
explosions which scarcely interrupt, and certainly do not stop, the 
progressive unrolling of the main theme. As a rule one genus in 
each restricted sub-tribe is closely allied to the immediate ancestor 
of the sub-tribe and, retaining the relatively primitive condition, 
physiological and otherwise, is capable of expansion, while the 
other more distant derivatives remain restricted more or less to 
their original sphere, Whether these restricted forms are really 
