OF THE PEEIJVIAN AIS^DES, 21 



developed several distinct species, oue of wliich, at least, has spread 

 northward into British North America. 



Among the Amei^ican genera that are conspicuous in the 

 Andean flora one of the most interesting is Baccharis. Among 

 some 280 described species which are scattered over every part of 

 South America, from the Straits of Magellan to the equatorial 

 zone, and which extend on tlxe west side of the continent to 

 California and Nevada, we find a surjjrising variety in habit and 

 in the form and arrangement of the vegetative organs, along with 

 a remarkable amount of imiformity in the reproductive organs, 

 which are constantly dioecious. I confess that the arguments 

 that have led some distinguished botanists to consider the great 

 family of Compositce as of comparatively recent origin aj^pear to 

 me altogether inconclusive. When I consider the vast variety of 

 forms which it includes, the degree in which some large groups are 

 localized in different regions of the earth, while others, such as 

 Senecio, have representatives in every zone, I shrink from the 

 conclusion that their origin can be, even in geological language? 

 at all recent. It is, of course, not inconceivable that plants which 

 we class together under the name Co?nj)ositce may have come into 

 existence hy different lines of descent through gradual modi- 

 fication from different ancestral types ; but when we consider 

 the general agreement in the structure and arrangement of the 

 essential organs, I think that the balance of probability inclines 

 decidedly towards the belief in a community of origin of all the 

 various existing forms. Be that as it may, we are, I think, 

 justified in looking to the mountain regions of South America 

 as the original Lome of many large groups, such as the genus 

 BacchariSy most of the Mutisiacece^ and many genera of other 

 tribes. 



I could not fail, while travelling in Soutli America, to reflect on 

 the probable origin of the types of vegetation which are common to 

 that portion of the continent and to distant spots in the southern 

 hemisphere, separated by wide expanses of ocean. The connec- 

 tion between these distant floras is proved by the presence of 

 closely allied, and CA'en of some identical species, belonging to 

 genera not known elsewhere in the world, and extends to many 

 forms that do not appear to be provided with special facilities 



for transport to a distance. 



I was struck hy several considerations which concur in indi- 

 cating the same probable explanation of these remarkable facts. 



