GENETIC CYTOLOGY IN SWEDEN 111 



polymorphy and its, in part, apomictical reproduction: the problems of the causes 

 of polymorphy and the lines followed by the formation of species. The section 

 Caninae, which contains the greatest part of the i?osa«vegetation of Europe, is 

 characterized by the peculiarity of showing in the reduction»division both gemini 

 and single chromosomes, usually 7 paired and 14, 21 or 28 unpaired, thus 

 representing an analogous chromosome*condition to what the writer stated in the 

 Drosera=bastard. In the other sections of Rosa only paired chromosomes are to 

 be seen, 7, 14, or 21 gemini. These latter have exclusively sexual reproduction. 



Triploid Roses, showing in the heterotypic division 7 paired and 7 single 

 are hybrids, derived from two sexual forms possessing respectively 7 and 14 

 chromosomes in the germ«cells. 



The Caninae are characterized by a quite peculiar type of reduction«division 

 in the pollen mother cells, which differ in certain respects from other types of 

 chromosome^distribution found in plants. The partners of the gemini pass to the 

 poles, while the single still remain in the equatorial plate, where they undergo 

 segmentation and later on begin their journey towards the poles. 



In the embryo^sac mother cells a very curious and interesting type of reduc» 

 tionsdivision occurs. In the anaphasis the partners of the gemini pass in normal 

 way to the poles, but usually all the singles pass undivided to one pole. The 

 result is that the one daughter^nucleus receives 28 chromosomes, the other only 7. 

 Eggs developed from such embryosacs containing 28 chromosomes are qualified 

 for fertilization, which can be proved by the chromosome sets in hybrids derived 

 from pentaploid species and normally sexual roses with 14 chromosomes. 



A cytological examination thus can be of use when the hybrid origin is to 

 be controlled. By a study of the chromosome^arrangement in the heterotypic 

 division it is also possible in certain cases to find out to which group of species 

 the parents of a hybrid belong. 



In the genus Crepis the writer has shown, that the different species are 

 characterized by very diflferent number of chomosomes: 3, 4, 5, and 21 in the 

 germ«cells. Hybridization experiments with Crepis»species with small num» 

 ber of chromosomes have been started by the writer. The dimensions of the 

 chromosomes are also very diflferent: in the nuclei with 3 chromosomes there are 

 1 very long, 1 short, and 1 chromosome of intermedial shape. In the species 

 with 21 chromosomes 7 sets of these 3 chromosome^dimensions clearly can be 

 distinguished. 



Finally it may be mentioned, that Heilborn by examination of a great num« 

 ber of Carex species has stated an interesting series of chromosome*numbers to 

 exist in this genus. 



