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SVENSK BoTANISK TipskKRIFT. 1920. Bp. 14, H. 2—3.
ON THE. CYTOLOGY, ‘OF; THE (GENUS I0
A PRELIMINARY NOTE.
BY
GUNNAR TACKHOLM.
Since the summer of 1917, I have been occupied with a study
on the cytology of the genus Rosa. The purpose of that study
was to learn to what extent the use of cytological methods of
research could be employed in the clearing up of the problems
that appear in this genus, distinguished by its enormous polymorphy
and its in part apomictical reproduction. I mean the problem of
the causes of the polymorphy, and in connection with that, ‘the
lines that the formation of species has followed; further the nature
of the apomictical reproduction and the occurrence of that pheno-
menon, partly within the whole genus, partly in such species that
are able to produce seeds both in a sexual and an apomictical way.
For getting a somewhat safe idea of such problems, the greatest
material possible is necessary for the investigation. Though my
material is far from being as complete as would be desirable, I,
however, have succeded in bringing together material representing
12 of the 15 sections into which CRÉPIN classifies the genus. Of
the three sections lacking, the first, Laevigatae, consists of only
one species, a native of China; the second, Minutifoliae, includes
two american species; the third of these sections, Bracteatae, con-
sists of two asiatic species. I have investigated most of the species
growing in the botanical gardens of Stockholm (Hortus Bergianus),
Uppsala, and the Kew Gardens, London, about 120 different forms
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