388 REVIEWS. 



" When we consider that, although subsidence has prob- 

 ably at various times separated the two portions of the con- 

 tinent, the highlands of Mexico and Central America have, 

 in all probability, served during long periods as a bridge 

 over which some portions of the mountain vegetation may 

 have been transferred from north to south, and vice versa, 

 we are led to feel surprise rather at the separations now ex- 

 isting than at the presence of many genera and of a few iden- 

 tical species in the flora of the Andes and that of the Rocky 

 Mountains. It is true that I have reckoned as Andean 

 genera and species many that extend northward as far as 

 Mexico ; and it may well be that that region, so rich in varied 

 forms of vegetation, is the original home of some that now 

 ajDpear to be more fully developed in the mountain ranges 

 of western North America. Among the widespread Ameri- 

 can types we must note two natural orders whose original 

 home may with some confidence be placed in the north- 

 western part of the continent. The PolemoniacecB, of which 

 about 140 species belong to that region, are represented in 

 the Andes by five sj)ecies of Gilia, one of Collonia, and by 

 the endemic genus Cantua. They have sent to the Old 

 AVorld two or three species of Phlox in northern Asia [we 

 believe only one, and that not far over the border], and a 

 single emigrant which has reached Britain, — the Jacob's 

 Ladder of old-fashioned gardens, — which maintains a strug- 

 gling existence in several isolated spots in Europe. The 

 other specially American family is that of the ILjdrophyUacecp, 

 of which 12 genera are known in North America, but which 

 is represented in the Andean chain by only four species of 

 Phacelia." The Loasacecv illustrate the opposite course of 

 migration. 



A list of the plants which Mr. Ball collected in tlie ujijicr 

 valley of the Rimac in the Peruvian Andes, with various an- 

 notations and the characters of some new species, concludes 

 the present interesting contribution to Andean Botany. We 

 believe that a second paper upon the sul)ject may be ex- 

 pected. Two or three comments upon individual plants of 

 the list will brinfj our review to a close. 



