304 steind6r steind6rsson 



perhaps the whole Ice Age in more or less isolated refugia. If we consider the 

 overwintering a reality, it remains for us to find evidence as to the existence of 

 such refugia and where they are situated. 



As we know, the prevaiUng opinion in the last century was that both Scan- 

 dinavia and Iceland were fully glaciated during the Ice Age, and consequently 

 that all biota must have ceased to exist there. According to this opinion, the so- 

 called tabula rasa theory, all biota of these countries must have immigrated 

 since the end of the Ice Age, or at the same time as the glaciers melted away. 



During the last fifty to sixty years various scientists have expressed their 

 doubts about the correctness of the tabula rasa theory, not only in Scandinavia 

 but also in Iceland. Arguments have been put forth that there is great likeU- 

 hood that some biota have hved there at least during the last glaciated period 

 of the Ice Age. 



Before discussing the possibihties of such refugia I will mention briefly the 

 hkehhood of natural immigration of plants to Iceland. We can imagine 

 three ways by which plants might have immigrated to Iceland, i.e. by ocean 

 currents, by air, and by help of migrating birds. 



Regarding immigration by the aid of ocean currents, a large-scale migra- 

 tion seems very improbable except in the case of some beach plants which are 

 more or less halophilous. The great distances from other countries make it 

 improbable that seeds might have kept their germinating power to any extent. 

 On the other hand, the beach of the country is very inhospitable, offering 

 unfavorable conditions for the seeds to take root. Furthermore, if a great 

 number of plants were brought to the country by the ocean currents, the Gulf 

 Stream on one side and the Polar Stream on the other, one might expect a 

 greater American element and especially a larger Arctic-Asian element than 

 is actually found in the flora of Iceland. 



There is a greater possibility that seeds have been carried by birds. I think 

 a considerable influx of plants by the help of birds is quite unlikely because of 

 the paucity of species with edible fruits. For example, of the many Rubus 

 species growing in the neighboring countries only a single one, R. saxatilis, 

 occurs in Iceland. As far as we know, the migration of birds to and from Ice- 

 land goes by way of the British Isles. If migratory birds were really an active 

 factor in the introduction of plants to Iceland, a greater affinity to the flora of 

 the British Isles would at least be very probable. 



Last to be considered is immigration by air currents, which in various 

 respects is more probable as we know that small particles can be carried for 

 long distances in the air. But if the greater part of the flora has been brought 

 to the country in this way, there should certainly be signs of it, e.g. in the 

 occurrence of an unusually great number of plants with seeds specifically 

 adapted to wind dispersal. 



Furthermore, it is probable that species endowed with such great capacity 

 for dispersal would spread over the entire country in a relatively short time, 



