130 P. A. ØVEN [1914 



enkelte, ineikværdige forhold med hensyn lil den japanske floras 

 utbredelsesforhold, og vi vil gjenhiide tilsvarende ogsaa paa andre 

 steder, i det hele tat overalt hvor indflydelsen af klimatologiske 

 vekslinger har gjort sig gjældende, i)aa en mere eller mindre 

 fremtrædende maate alt efter den maate hvorpaa topografiske 

 forhold har hidrat til at forslerke eller eHminere deres virkninger. 



SiNNOTT og Bailey har ganske nylig oflentliggjort et inter- 

 essant arbeide om »The Evolution of herbaceous Piants and 

 its bearing on certain Problems of Geology and Climatology « 

 (The Journal of Geology, Chicago, June 1915, Vol. 23, pag. 289 

 — 306). Her fremhæves den merkelige forskjel mellem Nordame- 

 rika og Nordeuropa med liensyn til plantevandringen før, under 

 og efter »istiden«. Og det er meget værd at lægge merke til, 

 hvad de to amerikanske forskere har at si: »In Nortli America, 

 especially in its eastern portion, the vegetation could easily mi 

 grate southward at the advance of the ice and return northward 

 at its retreat. In northern Europe, on the other hånd, the south- 

 ward escape of the vegetation was blocked, and it was crowded 

 against the Alps, the Pyrenees, and the Mediterranean, thus 

 suffering heavily by extinclion. These same natural barriers have 

 also prevented any considerable northward migration since the 

 retreat of the ice. The Vegetation of northern Europe today 

 seems, therefore, to be descended directly from that remnant 

 which was able to survive on the unglaciated portions of France, 



Germany, and England in faet, the flora of the Rockies 



presents a much closer resemblance to that of Euroi)e than 

 does the flora of the eastern part of the conlinent« (L. c. pag. 

 298—299). 



Her staar vi like overfor et andet, meget interessant fænomen, 

 nemlig at fjernere fra hinanden liggende egne kan vise slørre 

 biologisk likhet end nærmereliggende. Aarsaken dertil kan delvis 

 være at søke i specielle nutidsforhold med hensyn til klimatisk 

 likhet o. s. v. Ofte, og kanske som oftest, har vi at søke aar- 

 saken i en lang, mellemliggende utvikling af klimatologisk og 

 topografisk art. 



SiXNOTT og Bailey sier, at if the flora of northern Europe 

 is indeed typically representative of that which flourished near 

 the ice front during glacial times, the proportion of woody forms 

 within it affords us a valuable index as to climatic conditions 

 during the height of the ice age. The facts seem to indicate that 

 when the ice sheet had reached its greatest extent the country 

 in its immediate front was neither a barren arctic tundra, as 

 has sometimes been supposed, nor covered with a luxuriant 

 temperate vegetation; but that the climate in general resembled 

 that of the lower portions of the Alps or the Rockies today, 



