fulltext - DiVA

126 Bertil LinäquistEurope and var. alpestris in the N orth and on the European mountains. Theglaciätions then have destroyed the main bulk of the old population and severedthe elirnatic extren1es on the coast of the Arctic Ocean (ad var. alpestris) fromthe extremes south of the ice border (ad var. rariflorus and fuscoater). In theunglaciated areas north and south of the ice border the populations of theseextreme biotypes thus have been to a certain degree stabilized and have developedtheir present characters.When the last glaciation was ended these varieties have had possibilities ofspreading within the previously ice-bound districts. The two types exclusivelyconfined to the ice border in the mountains and in the Arctic, var. alpestris andvar. Marshallii, have not, in common with so many other glacial relics, shownany great capacity for spreading outside the glacial refugia (rigid plants, cf. HUL­TEN 1937); they have also in following periods, probably as a result of biotypepauperisation, been confined to the far northern and arctic areas and to the highestEuropean mountains. The variety rariflorus, on the contrary, has migrated fromits positions south of the ice belt northwards, and in Europe also westwards, andspread over very large areas in the northern hemisphere. The N orth-Scandinavianpopulations of this variety who have survived the glacial period in the far North,however, seem to have been incapable of the same great spreading - just asthe two arctic glacial relics mentioned above. The variety fuscoater has likewisespread very profusely after the last glaciation, invading Seandinavia fromsouth-east, and concentrating in the same area as var. rariflorus. In such areaswe find an intense erossing going on between them, which to-day has madethe types indistinct (cf. LINDQUIST l. c., p. 337 f.).In conclusion it may be said that within the districts where there still occursbut one of the varieties under discussion, such as var. rariflorus in certain districtsof N orth America, var. alpestris in arctic N orway and in the European mountains,var. Marshallii in Scotland and var. fuscoater in Hungaria, western Germany andFrance, the types and type differences are maintained to a considerably greaterdegree than where they have come in contact with one another after the last glaciation.N on e of these varieties, which ma y be assumed to have differentiatedduring the Quaternary glaciations, seems thus to have been stabilized to such anextent, that sterility boundaries have been created, separating the varieties asdifferent species, and when, after the last glaciation, the isolation was broken, thespecies J. alpinus seems, through lively crossings within the populations in thepreviously glaciated districts, to have developed towards an again less differentiated;polymorphous type, in the same way as has been assumed by HULTEN(l. c., p. 47) for other circumpolar plants of the northern hemisphere.