416 ORIGIN OF LIFE IN AMERICA 



Mountain arctic alpine region reappear in the extra-tropical 

 Andes, being, so far as is known, wholly absent from the 

 Mexican Mountains as well as from the tropical Andes. 

 Among these Professor Bray mentions particularly Gentiana 

 prostrata, Trisetum subspicatum, Primula farinosa and its 

 variety magellanica, Draba incana, Alopecurus alpinus, Saxi- 

 fraga caespitosa, Polemonium microcanthum and Collomia 

 gracilis. Dr. Stapf kindly drew my attention to another 

 instance, namely, to the occurrence on the mountains of 

 Argentina, at a height of 10,000 feet, of the typically arctic 

 genus of grasses Phippsia. The similarity in the flora of the 

 two regions is by no means confined to mountain forms. 

 Some species of the western plains of North America also 

 reappear in the extreme south of South America. Thus the 

 monotypical saxifrage Lepuropetalon, a peculiar and some- 

 what abnormal genus, grows in damp low-lying meadows in 

 Texas. Yet far south on the coast of Chile the same species, 

 Lepuropetalon spathulatum is to be met with. 



A few of these plants may possibly have been casually in- 

 troduced from the northern locality to the southern. But in 

 most cases, Professor Bray * thinks, we have to deal with 

 forms which were connected by a remote ancestry, and which 

 flourished at a time and under conditions permitting a more 

 general distribution. 



What these conditions were like he does not venture to sug- 

 gest, but a direct land bridge between western North America 

 and Chile probably existed, as I suggested, in late Cretaceous 

 and early Tertiary times. To it, I think, the relationship 

 of the floras of these two widely separated areas to one 

 another, is mostly due. Whether many species of plants 

 have persisted to the present day from such remote times 

 we do not know. Some no doubt have, and, as already 

 stated, others, among them those alluded to, may have 

 done so. A large portion of this old western land, with' 

 its mixture of a southern and northern fauna and flora, 

 evidently remained above sea-level until a much later geo- 

 logical period. The evidence derived from certain relict 

 land -areas of this Pacific land belt clearly shows that a 



* Bray W/L., " Belations of North American Flora," pp. 709716. 



