6 
James Small. 
subject which to my knowledge have been propounded is that a 
race of plants, be it tribe or genus or species, in its period of full 
vigour, is widely dispersed, accommodates itself to a great variety 
of climatological, physical or other external influences, is numerous 
and varied in subordinate races, as well as individuals, these subordin¬ 
ate races, especially those immediately subordinate, not being separ¬ 
ated by wide structural gaps, and not having acquired any marked 
local characters, but for the most part passing, as it were, into each 
other, their respective distinctive characters not having yet acquired 
any marked degree of correlation. On the other hand, a race in a state 
of decay is represented by subordinate races very distinct in 
structural characters, of restricted areas, and requiring for their 
preservation special climatological or other physical conditions, and 
consequently comparatively few in number .... Old decaying and 
apparently expiring races may, however, in some of their branches, 
owing perhaps a slight change in constitution, habit or external 
circumstances, start into new life .... These young progressive races 
will be very prolific, ready colonisers; and their subordinate races 
will be generally numerous and so blended together as to defy all 
positive determinations of their limits, and be variously estimated 
as subgenera, sections, species, subspecies or varieties. ” Again 
writing of the sections of Vernonia (I, 7, p. 393) he says “ the section 
Lepidaploa, which, rather from its wide geographical range and 
connections than from its happening to include the species first 
taken as the type, may be conjectured to be nearest to the original 
form. ” 
These views, it will be seen, form what is probably the best pre* 
Willisian account of the relation of Area to Age. But, whereas 
these are suppositions fairly obvious but unproved, the hypothesis is 
raised to the status of a fundamental law by the statistical proof 
furnished by Willis for age within a given country, and its proved 
extension to absolute age and total area seems to be only a question 
of time and application. 
B. Geographical Distribution of Senecio. 
The Senecioneae are indicated in previous chapters as the 
primitive tribe; the distribution of the chief genus, Senecio , is 
therefore of fundamental importance. If the numerous species of 
Senecio were confined to one locality or even to one continent, it 
would be difficult to uphold the view that they had been the source, 
for example, of the Arctotideae in South Africa, the Vernonieae in 
