956 PATAGONIAN EXPEDITIONS: BOTANY. 



the butterflies on the borderland of North and South America, a writer 

 with the familiar initials E. B. P. supplies us with very pregnant sugges- 

 tions in the same directions. 1 It is there shown that the U-like shape of 

 the borderland about the Gulf of Mexico and the Caribbean Sea has had 

 a special influence on distribution. Not only have many southern forms 

 come northwards ; but in turn northern forms have migrated southwards ; 

 oscillations of the backbone of the New World, accompanied by changes 

 of climate also serve as determinants of the direction and result of the 

 migrations from colder climates. Gray and Hooker gave special empha- 

 sis to the return northward of plants that had previously moved south- 

 ward ; but it would appear that some individuals had in Glacial times 

 gone so far south as to leave themselves no room for repentance on the 

 return of warmer times. They went further south, hugging the Andes, 

 and finally a selection of them reached Patagonia. 2 



It is to be remembered that in such cases the immigrants frequently 

 change by way of adaptation to the new homes ; their resemblance to the 

 old ancestral forms will be generic rather than specific. Such a form as 

 Braya presents a series of specific forms, reaching from the Alps of 

 Europe by the Caucasian range, with a couple of species in the Himalaya 

 region ; so on through Siberia and across Bering Strait to Alaska and 

 the mountains of Western America, down to southern Chili and Patagonia ; 

 reappearing again in New Zealand ; almost belting the world. 



We have been anticipated to some extent on this subject by Professor 

 N. L. Britton, who addressed a meeting of botanists at Buffalo on the 

 influence of the mountains of Asia in plant-distribution. Mrs. Britton 

 informs us that a large number of our American Mosses occur as well in 

 Cashmere Valley. 3 Wallace had something of the kind in view when in 

 his work on Island Life he referred to the mountains of the Oriental 

 islands as receiving contributions carried by the winds from the Him- 

 alayas. Asa Gray in his paper on the Flora of Japan (Scientific Papers, 

 ii, p. 125), finds many species common to Japan, the Himalayan region, 



1 Nature, Nov. 13, 1902. (Presumably E. B. Poulton.) 



2 See Schimper (Pere), Paleontologie Vegetale on the Glacial and Post-glacial Flora of Europe. 



3 Mrs. Britton refers to a statement by V. F. Brotherus in the Contribution on the Bryological 

 Flora of the northwestern Himalaya, Helsingfors, 1898. The list includes 49 genera and 96 

 species, all mosses which are also found in North America ; the altitudes vary from 6,000 feet in 

 the valleys to from 20,000-26,000 feet on the highest mountains, and the flora is similar to that 

 of the mountains of Europe and temperate North America. 



