1925] Mann: Chromosome Number and Individuality in the Genus Crepis 307 



Crepis japonica (N = 8) (fig. 17) and bulbosa (N = 9) (fig. 18) are 

 rather similar in chromosome individuahty, but are totally different 

 from all the rest of the species studied in chromosome number and size. 



japonica 15.7 13.5 12.2 11.5 10.8 10.0 9.7 9.2 



bulbosa 13.9 12.8 12.1 11.7 11.1 10.6 10.1 9.6 8.6 



It is, of course, possible that japonica might have been derived from a 

 species like tectorum by cross-division of every chromosome, or vice 

 versa. When we test this hypothesis by adding the averages for the 

 two largest, the next two, etc., of japonica together, the results are 

 rather striking. 



japomca. 

 tectorum.. 



+1.1 +0.5 +0.6 +1.7 



It is at least obvious that tetraploidy could not explain the chromosome 

 individuality of japonica while cross-division might do so. 



Crepis sieberi (fig. 19) is the only species so far studied which has 

 six pairs of chromosomes. It looks as if it might have four pairs of 

 short chromosomes: 



capillaris 26.2 20.4 14.8 



17.7 + 16 + 15.2 + 12.5 

 sieberi 26.8 21.4 ■ =15.3 



+0.6 +1.0 +0.5 



or two intermediate and three short pairs: 



capillaris.... 26.2 20.4 14.8 



21.4 + 17.7 16+15.2+12.5 



sieberi 26.8 =19.5 ■ ■ =14.6 



2 3 



+0.6 -0.9 -0.2 



Crepis pulchra (fig. 21) and dioscoridis (fig. 4) are very similar to 

 one another in chromosome length. 



pulchra 



dioscoridis 



Difference 0.8 1.3 0.6 



C. sibirica (fig. 23), with five pairs, resembles pulchra and dioscoridis 

 in choromosome measurements, and the average length of the two 

 longest chromosomes, 36.5, indicates that it may have two instead of 

 one of the longest type of chromosome. 



