Notice of a Flora of North America. = —- 283 
arbitrary arrangement of them in separate series. In some sort, 
these do no doubt exist, but the differences are scarcely more 
than matters of degree, and hence, where extensive means. of 
comparison are not within reach of the student, the appreciation 
of the terms necessarily employed to describe these variations, 
becomes mere matter of opinion, and therefore open to misa 
hension. These difficulties, inseparable from the nature of the 
Case, are not within the control of any systematic writers, and 
we believe that the present arrangement will not disappoint the: 
hopes of the authors, who “trust that most of our indigenous. 
Asters may be satisfactorily identified by the student.” .* * 
We shall only further notice the kindred. and very difficult 
genus Lrigeron, which we shall do in the succinct and philo- 
nei observations of Drs. Torrey and Gray : 
“Tt appears — to us impossible to effect generic divisions among these 
plants, by characters derived from the single or double series of rays, 
or r fro the simple or double pappus, or by any combination of these. 
or 
Aster ; but the alpigenous Asters almost aes two genera.” jal 
et 
“The genus has been entirely remodelled, and bears ample ¢ es. 
timony, no less to the science than to the unwearied | patience 
which have been devoted to the subject. We feel justified in- 
deed, in extending this encomium, not merely to the last num- 
‘, but also to the entire work of Drs. Torrey and Gray, so far 
as | it is before the public ; and we trust, for the sake of natural 
science, more especially that branch of it so much below its Just 
- appreciation in our own country, that this most valuable contri- 
b ation towards its elevation, may be carried to completion by pe 
laborious and talented authors. TC. 
; i hci tit ail sa Arild z Joe 
ais < hie pth SRD CO Se ee Gy Ba ae . 
