16 
James Small. 
Senecio it is clear from the detailed study of the genus, of which the 
above is a very meagre and fragmentary account, that its history 
can be epitomised somewhat as follows. The genus, arising in 
the Andes, spread comparatively rapidly (cp. Willis, 82, p. 342.) 
along the unwooded regions of the mountain ranges of the world; 
while the floral structure which characterises the genus remained 
practically the same, the extreme diversity of conditions combined 
with a marked constitutional instability in the vegetative structure 
producing in each region several distinct variations in habit and a 
large number of local species. Because of this free reaction of the 
vegetative part of the Senecio plant to its environment there is no 
species which completely covers the range of the genus. 5. vulgaris 
is cosmopolitan but has been largely introduced from Europe. 
Instead of a species we have the weedy type , which is cosmo¬ 
politan, and also various species with wide areas of distribution, 
a few of which taken together cover the chief regions occupied by 
the genus. 
Finally it is abundantly clear that the geographical distribu¬ 
tion of Senecio is quite in accordance with the view that a number 
of tribes have arisen from this genus in widely separated regions of 
the world. 
C. Geographical Distribution of the Tribes. 
Although not up-to-date, Bentham’s statistical summary (I, 7) 
of the geographical distribution of all the genera of the Com- 
positae remains sufficiently accurate for a general view of the 
distribution of the tribes and sub-tribes. The centres of origin 
and paths of migration, however, cannot be deduced from his 
table with any certainty. An analysis was therefore made of 
the distribution of some fifty widespread genera, including 8,600 
species, by similar but not such detailed methods as were used for 
Senecio. Maps were made and the centres of origin and paths 
of migration were traced. In these maps a line around a country 
with a number included is used where the distribution within 
the country is not given in detail, and many dots are used where 
the map is too small for the useful employment of lines which 
indicate wider areas. Genera from all the tribes except the 
Calendulese and Arctotidese were examined. Bentham’s table was 
used in some cases to elucidate the centres of concentration of the 
sub-tribes and the results will now be discussed. 
Senecionece. As the basal tribe the Senecionese have been 
studied specially and the distribution of all the genera in each 
