304 University of California Publications in Agricultural Sciences [Vol. 2 



Setosa (fig. 3), like neglecia, differs little from capillaris in total 

 length. It contains, however, only one pair of chromosomes shorter 

 than any in capillaris; otherwise it is rather similar to it. 



capillaris 26.2 20.4 14.8 



setosa 22.3 17.8 14.0 9.1 



-3.9 -2.6 -0.8 +9.1 



It has already been noted that the longest chromosome of setosa has 

 a semidetached tip by which it may be recognized. This tip is usually 

 at an angle to the main portion of the chromosome. In the figures 

 given above the longest chromosome of setosa appears to have lost a 

 portion of its length, while another pair of chromosomes averaging 

 about ten units has been added. It is also possible that the longest 

 chromosome has cross-divided, and that the peculiar chromosome of 

 setosa really corresponds to the intermediate of capillaris. 



capillaris 26.2 20.4 14.8 



setosa 17.8+9.1=26.9 22.3 14.0 



+0.7 +1.9 -0.8 



If either of these possibilities represented the whole truth concerning 

 the difference between the two species, we should expect reduction to 

 be fairly normal following hybridization. As a matter of fact, no 

 pairing occurs in the Fi setosa (N = 4) X capillar is (N = 3) (Collins and 

 Mann, 1923), and as a consequence gametes are formed with 3, 4, and 

 6 chromosomes as shown by five plants (backcrosses to setosa), which 

 have 7, 8, and 10 somatic chromosomes. It seems possible that new 

 types differing in number and combination of chromosomes may be 

 obtained by selfing such plants as the backcrosses with ten chromosomes. 



Crepis parviflora (fig. 8) has a chromosome individuality much like 

 that of setosa; the longer chromosome, however, averages slightly longer 

 and does not appear to have a semidetached tip. 



setosa 



parviflora 



+3.0 +2.7 +0.4 +0.7 



It is evident that parviflora is more similar to capillaris than setosa, 

 but like setosa it has an additional short pair of chromosomes. 



capillaris 26.2 20.4 14.8 



parviflora 25.3 20.5 14.4 9.7 



-0.9 +0.1 -0.4 +9.7 



The first hypothesis for setosa appears to be the more probable for 

 parviflora. If it were true, one would have to account for the additional 

 chromosome of 9.7 units by hybridization between two such forms as 



