Rit Landbúnaðardeildar : B-flokkur - 01.05.1947, Page 22

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árvogur in the vicinity of Reykjavík in the South-West of Iceland (Thor-
kelsson, 1935), a rather large number of Ieaves of species common in
Iceland at present have been observed. And even some of the Icelandic
species appear to have grown in Icelandic soil at least since the Miocene,
e. g. Betula callosa (cf. Lindquist, 1946, 1947).
Summary.
The present paper is the first one in a planned series on the origin of
the Icelandic. flora. It deals with the cvtology and geography of Cakile.
The European species C. maritima L„ which is met with on European
beaches and islands to the Faeroes in the west, is found to be diploid
with 2n = 18 chromosoines, but the American species C. edehtula
(Bigel.) Hook., which is met with in three subspecies, one of which is
found at the east coast of North-America from Yukatan up to Labrador
as well as in Iceland and the Azores, is found to be tetraploid with 2n = 36
chromosomes. On the basis of studies on the meiosis of the tetraploid
species it is assumed that it should be regarded as an autotetraploid.
In the discussion, the hypothesis is set forth that C. edentula has
dispersed to Iceland from America bv aid of the Gulf Strearn. It is
assumed that its dispersion has taken place after the end of the last
glaciation and not before the coast line had becoine almost the saine
as it is at present.
The origin of the Icelandic flora is discussed to soine extent. Up to
30% of the present flora of higher plants may have been imported by
man during the last 1100—H200 years. The writers are inclined to
regard it as a very slight possibility that some few of the species at
present found on the island have dispersed from other countries in
recent times by air currents or birds, but a small number of species may
have migrated by sea currents. The writers, however, are not inclined
to assume that more than 15% of the present flora elements have
migrated in this way after the last glaciation. At least 55% of the present
flora are suggested to have survived the latest ice invasion and perhaps
the whole Ice Age in Iceland. The survivors are classed into three groups
according to the nature of their present distribution and their proposed
genetical causes, and some species are named as examples of survivors
of these three groups.