DISTRIBUTION OF TRIBES, 403 
have considered to be in themselves of generic importance, the 
following are more or less connected with geographical distribu- 
tion :— 
(1) The section Alpigenia, ranging over the mountain-regions 
of the northern hemisphere, and including the above-mentioned 
transtropical African species, with the achenes and pappus of the 
typical Asters, acquires the habit and involucres and, in some 
measure, the increased numbers of ray-florets of a corresponding 
mountain group of Erigeron inhabiting the same regions, and thus 
to a certain degree connects the two genera. 
(2) The Andine section Noticastrum, consisting, as far as known, 
of two species only, with a slight modification in the ribs of the 
achenes, but with the pappus and other essential characters of 
Aster, closely connects the genus with the Andine group of 
Erigeron; whilst the nearly related section Heterastrum, also 
South American and chiefly extratropical, approaches another 
South- American set of Erigeron, even in the pappus, and has been 
alternately placed in both genera. So, also, the section Oxytripo- 
lium, with very few species dispersed over North and South America, 
connects the same set of Erigerons with the section Orthomeris of 
Aster. This latter section, chiefly differing in the involucre, 
although present in North America, has been much more 
developed and become much more varied in Asia. 
(3) Tripolium and Galatella are Europseo-Asiatie forms charac- 
terized chiefly by the reduction, sterility, or disappearance of the 
florets of the ray, towards which there is very little tendency in 
N. America, although Galatella itself is there represented by one 
species. Tripoliumis a single very variable species with a peculiar 
involuere, the ray-florets sometimes abundant and conspicuous, 
sometimes very few or absolutely none. Galatella has the invo- 
lucre of the section Orthomeris (the one most abundant in Asia) ; 
but the female florets are usually sterile or have not even a rudi- 
mentary style, or in some species are usually entirely deficient. 
For the Jatter case the genus Linosyris was established; but it 
has been proved that the Old- World species sometimes acquire the 
ray and become true Asters of the section Galatella. The American 
species associated with Linosyris on account of the absence of ray- 
florets belong rather to the Solidago group to be presently referred 
to. 
Close around Aster are two small genera belonging geographi- 
eally to parts of the main region of that genus, and which, even 
