Flóra: tímarit um íslenzka grasafræði - 01.01.1963, Side 145

ploids based on their greater genetical variability as proposed by Melchers (1946)
and supported by Löve & Löve (1949) in connection with their critical review of
the geobotanical significance of polyploidy. That explanation easily accounts for
the apparently greater resistance to the environment shown in the occurrence of
many polyploids in old floras tltat have liad to survive the extreme conditions of
the Pleistocene glaciations in the northlands, where only the selectively strongest
could persist. It also explains the high frequency of polyploids among the now re-
lict Pteridophytes of which the diploids and lower polyploids seem to ltave been
selectively weakest. And, finally, this is also the most plausible explanation of the
recent finding by Mangenot & Mangenot (1962) that the tropical African flora is
characterized by a very ltigh írequency of ancient polyploids, the diploid ancestors
of which have long sincc succumbed to selection.
It is, finally, pointed out, that the low frequency of endemics on arctic and
subarctic islands with remnants of old floras left by the Pleistocene glaciations may
well be the result of the same resistance to selection that has resulted in their high
frequency of polyploids.
RITSKRA.
Hagerup, O. 1928: Morpliological and cytological studies of Bicornes. — Dansk Bot. Arkiv
6,1: 1-27.
— 1932: tíber Polyploidie in Bezielumg zu Klima, Ökologie und l’hylogenie. — Hereditas
16: 19-40.
Löve, Á. 1953: Subarctic polyploidy. — Hereditas 39: 113—124.
— 1959: Origin of the arctic flora. — Publ. McGill Univ. Museum 1: 82—95.
Löve, Á. & Löve, D. 1949: Geobotanical significance of polyploidy. I. I’olyploidy and lati-
tude. — Portug. Acta Biol. (A), R. B. Goldschmidt Vol.: 273—352.
— 1953: Geobotanical significance of polyploidy. — Proc. VI Intern. Grassl. Congr. (1952):
240-246.
— 1957: Arctic polyploidy. — Proc. Genet. Soc. Canada 2: 23—27.
— 1963 (ed.): North Atlantic Biota and Their History. — Oxford.
Mangenot, S. & Mangenot, G. 1962: Enquéte sur les nombres chromosomiques dans une
collection d’espéces tropicales. — Revtie Cytol. Biol. Végét. 25: 411—447.
Melchers, G. 1946: Die Ursachen fur die bessere Anpassungsfahigkeit der Polyploiden. —
Zeitschr. f. Naturforsch. 1: 160—165.
Mulligan, G. A. 1960: Polyploidy in Canadian weeds. - Canad. Journ. Genet. Cytol. 2: 150
-161.
Reese, G. 1961: Karyolype and ])lanl gcogiaphy. — Recent Adv. in Bot.: 895—900.
Stebbins, G. L. 1950: Variation and cvolution in plants. — New York.
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