1925] Mann: Chromosome Ntimber aiid Individuality in the Genus Crepis 305 



neglecta and capillaris. The hybridization results for setosaXcapillaris 

 given above indicate that new types with new combinations of chromo- 

 somes may arise in this manner. It will be interesting to observe the 

 results of crossing setosa and par vi flora. 



Bursifolia (fig. 9) appears to have an extra element of the size of the 

 intermediate chromosome of the capillaris series: 



capillaris 26.2 20.4 14.8 



22+19.5 

 bursifolia 24.3 =20.7 12.7 



-1.9 +0.3 -2.1 



It's average total length is 17.1 units longer than that of capillaris. 

 Crepis taraxacifolia (fig. 10), tectorum (fig. 5), and blattarioides (fig. 

 11) have very similar chromosome groups. 



taraxacifolia 26.1 23.3 21.2 17.8 



blattarioides 29.0 23.8 20.6 17.7 



tectorum 28.1 23.2 20.2 17.2 



All the chromosomes of these three species tend to average slightly 

 larger than those of capillaris, but the differences do not greatly exceed 

 those of the different averages for capillaris. If we suppose that the 

 intermediate chromosome of capillaris has been duplicated in this 

 group of species, the correspondence is somewhat bettered. 



Average of taraxacifolia, tectorum, and 



blattarioides 27.7 22.05 17.6 



Average of capillaris 26.2 20.40 14.8 



+1.5 +1.65 +2.8 



It is obvious that the relative lengths of the chromosomes in these 

 three species are very similar to those in capillaris. 



Tectorum and capillaris were repeatedly crossed by Collins (1920), 

 but the Fi developed only as far as the cotyledon stage. Tliis indicates 

 an incompatibility of the chromosomes or cytoplasm hard to account 

 for on the basis of mere addition of similar material, especially when one 

 considers that trisomic forms which come to maturity appear to be not 

 uncommon among plants and animals. It will be very interesting to 

 know whether others of the group of species indicated above will behave 

 like tectorum in crosses with capillaris, and whether they will intercross. 



Aspera (fig. 12) is like the group discussed above except that the 

 longest chromosome appears to be rather short. 



capillaris 26.2 20.4 14.8 



21.5 + 19.7 

 aspera 23.9 =20.6 17.5 



-2.3 +0.2 +2.7 



