— 388 — 



Fig. 8 



Number of 

 chromosomes 



Chromosomes lost 





in heterotyp. 

 division 



in hoinotjT). 

 division 



Tetrad a 



— b 



— C 



— d 



— e 



14 + 14 

 



11 + 11 

 .... 



1 



9 

 1 



4 + 4 





- - f i 





1 



2 + 3 



Artificial hybrid 



There is a large accordance and similarity in the nuclear 

 divisions between the artificial hybrids and the suspected, spon- 

 taneous hybrids. 



When 13 tricolor- chromosomes and 17 arvensis-chromosomes 

 are brought together, they behave in different ways in the hete- 

 rotypic metaphasis. They can form either 15 bivalents, 14 bivalents 

 and 2 univalents or 13 bivalents and 4 univalents. The most 

 frequent is 14 bivalents. We must suppose that 13 tricolor-chro- 

 mosomes join with 13 arvensis- chromosomes and, in addition, 2 

 arvensis- chromosomes join with each other forming the 14th pair. 

 The univalent chromosomes in some cases go to different poles, 

 in other cases to the same pole both, and in other cases again 

 one or more of them are lost in the first or in the second division. 

 Most frequently they are lost in the homotypic division. We 

 must suppose that they can be lost during the vegetative mitoses 

 too (Fig. 7 d, g and h). As I never yet have found tricolors with 

 less than 13 chromosomes, I must suppose that pollen or eggs 

 with less than this number, or the zygotes with less than 26 chro- 

 mosomes degenerate. 



This type of distribution of chromosomes after crosses was 

 not previously known. The only one it resembles is the distribu- 

 tion in F 2 of a cross between Solanum nigrum diploid x tetraploid (72 

 chromosomes x 36 chromosomes) according to a discourse deliv- 

 ered by H. Winkler in the Deutsche Gesellschaft für Vererbungs- 

 wissenschaft (H. Nachtsheim 1921). Fj of this cross in its vege- 

 tative cells has 108 chromosomes, but in the reduction division it 

 exhibits 54 bivalents, so that all the 36 chromosomes of the diploid 

 parent must unite with 36 from the tetraploid and the remaining 

 36 from the tetraploid must unite mutually to form 18 pairs. 



