Svensk Botanisk Tidskrift. 1920. Bd. 14, H. 2 — 3. 



ON THE CYTOLOGY OF THE GENUS ROSA. 

 A PRELIMINARY NOTE. 



BY 



GUNNAR TÄCKHOLM. 



Since the surnmer of 1917, I have been occupied with a sludy 



011 Ihe 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, Laeuigatae, 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 



