1929] BabcocJc-Clausen : Meiosis in Crepis 415 



and one with a pure set of hursifoUa chromosomes among 40 to 50 

 florets. If about the same amount of pollen — good and bad together — 

 were available for each ovule, or if F^ were backcrossed with pollen 

 of one of the parent species, we should expect at least 4 or 5 per cent 

 of the florets to set seed giving either pure aspera, pure hui'sifolia, 

 or the Fi hybrid type again. But among the gametes calculated to 

 contain either aspera or hursifoUa chromosomes alone, some might 

 contain chromosomes that have been changed by crossing over, so 

 that the balance has been disturbed. The Crepis chromosome groups 

 do not seem to withstand even a small change in balance as well as 

 do, for instance, the chromosome gi'oups in certain Viola hybrids (J. 

 Clausen, 1926). All these things ought to account for the small 

 degree of fertility. Haney estimated the fertility to be about 3-4 

 per cent by open pollination. No seeds have been collected. 



The type of meiosis described for this Crepis hybrid is dissimilar 

 to the type described by M. Navashin (1927) for the hybrid C. capil- 

 laris X aspera. In this last-mentioned hybrid lengthwise splitting 

 apparently is a common phenomenon. 



2. Crepis taraxacif olia X C. tectorum. — Meiosis in this hybrid is 

 similar in general to that in the hybrid just described. Of C. taraxa- 

 cif olia X tectorum only iron-acetocarmine smears have been used and 

 only from material fixed in Carnoy's fluid by Ilollingshead. An 

 attempt to make permanent, sectioned slides from this fixation was 

 unsuccessful. No differentiation could be obtained either with iodine- 

 gentian violet or with Heidenhain's iron-haematoxylin. The iron- 

 acetocarmine could be used but did not give good differentiation. 



From table 1, page 412, it will be seen that the most common 

 situation met with in heterotypic metaphase was 2 bivalents and 4 

 univalents, while 70 per cent of heterotypic metaphases are irregular. 

 Detachment of chromosomes during meiosis I is common and there 

 are 63 per cent of irregularities in the tetrad phase. Plate 61, figures 

 42-45, gives different heterotypic metaphases with from 4 to 2 pairs 

 of chromosomes. No visible difference in size is here discernible 

 among the chromosomes. Plate 61, figure 46, shows a regular, and 

 figure 47, an irregular homotypic anaphase, while figure 48 is a 

 schematic figure drawn to show how the chromosomes in figure 47 

 would be distributed among the nuclei a little later. Figures 49 to 

 54 show how the tetrad phase looks in this hybrid. Figure 49 is a 

 nonad. As only 16 chromosomes will be present in the nine nuclei 

 altogether it is not hard to figure out how many chromosomes will 



