Rit Landbúnaðardeildar : B-flokkur - 01.05.1947, Blaðsíða 15

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At present, about 510 species of higher plants, except the genera
Hieracium and Taraxacum, are found in Iceland. Preliminary studies on
apophytic and anthropochorous plants, made by the present writers
during the last summer, reveal that hetween 25 and 30% of the present
flora of Iceland might have been imported by man.
The Icelandic species not imported by man may have dispersed either
before the island became isolated from other countries, i.e. long before
the Ice Age, or they may have dispersed after the end of the last glaciation.
Dispersion of seeds across the Oc.ean as it has been since before the
heginning of the Ice Age might, theoretically, have been by the aid of
winds, birds or sea currents. Some considerations as to these three pos-
sibilities may be made at present.
Concerning the dispersion by wind, it has been demonstrated by some
authors (Falck, 1927; Stakman, Henry, Curran and Christopher, 1923;
Meier, Stevenson and Charles, 1933; Shitikova-Rusakova, 1927; Peter-
son, 1931; cf. Wolfenbarger, 1946) that the spores of Cryptogams may
be carried by air currents over wide areas, and pollen of some higher
plants has been found to be carried by the air for a distance up to 1000
km or even more (Aario, 1932; Erdtman, 1921, 1924, 1936, 1937, 1943;
Hesselman, 1919; Jessen and Rasmussen, 1922; Malmström, 1923;
Steleanu, 1932; MacQuiddy, 1935; Meier and Artschwager, 1938; cf.
Wol^enrarger, 1946). However, no plant species is able to disperse only
as a pollen grain.
The seeds of plants are much heavier than the pollen grains, and only
a relatively few species develop seeds that are carried long distances by
the wind. It must be regarded as satisfactorily demonstrated, that the air
currents are able to disperse the seeds of different species over wide areas
round their origin (cf. Gulich, 1932; Heintze, 1932—1936; Kerr, 1931;
Metsavainio, 1926; Simpson, 1932; Ulbrich, 1928; Vogler, 1901; Warm-
ing, 1902, 1903; Wulff, 1943), but investigations performed by a number
of scientists seem to indicate that the wind is only abie to carry seeds
a relatively short distance and never across the ocean. De Candolle
(1855) concluded that seeds were never transported by wind from Ireland
to England nor from England to France or even from Sardinia to Corsica.
According' to Wulff (1943) almost 60% of the higher plants of the latter
island are endemics. Kerner (1871) pointed out that at least the seeds of
Pinus as well as the seeds of most of the species of Compositae are only
able to fly over a relatively small area, although they are specially adapted
for flight. According to Schmidt (1918) seeds and fruits adapted for
wind-dispersal may be carried by air currents not more than a few kilo-
meters and sometimes only a few meters. Rentham (1873) and Ridley