1925] Mann : Chromosome Number and Individuality in the Genus Crepis 311 



SUMMARY AND CONCLUSIONS 



1. With the exception of negleda and possibly setosa, all the species 

 of Crepis studied show significant increases in total length of the chromo- 

 some complex over that of capiUaris, the single species with three pairs 

 of chromosomes. 



2. Generally speaking, increased number is associated with 

 increased total length, but there are certain exceptions. 



3. In so far as studies on chromosome individuality can determine, 

 five of the species with four pairs of chromosomes might have two 

 pairs like the intermediate chromosome of capiUaris. 



4. In Crepis negleda (N = 4) the two shortest chromosomes might 

 have been derived by cross-division of a chromosome of the length of 

 the intermediate chromosome of capiUaris. 



5. Crepis setosa (N = 4) and parviflora (N = 4) are very similar in 

 total length and quite unlike all of the other species. 



6. Crepis dioscoridis (N = 4) and pulchra (N = 4) have a long pair 

 of chromosomes which is not represented in capiUaris or in the other 

 four chromosome species. It is possible that it might be a multiple 

 chromosome. That this difference in length is not due to a difference 

 in physiological condition or to error is shown by the fact that it is 

 maintained when the dioscoridis chromosomes are in setosa cytoplasm 

 in an Fi between these two species. All the chromosomes of these two 

 species can be distinguished in this Fi. 



7. Aurea stands out among the species with five pairs because of 

 its lack of an element like the longest chromosome of capiUaris. The 

 complexes of rubra, foetida, and alpina might all have been derived by 

 duplication of certain chromosomes of capiUaris. Sibirica seems to 

 possess two chromosomes like the large element of dioscoridis and 

 pulchra. 



8. The single species with six pairs, sieberi, has chromosomes which 

 are enough like those of capiUaris in length to have been derived from 

 it by chromosomal duplication. There appear to be but one pair 

 of the large and the intermediate types, and four pairs like the short 

 chromosomes. 



9. Japonica with eight pairs might be derived by cross-division of 

 all chromosomes of a species like tectorum. 



10. Bulbosa (N = 9) has short chromosomes like those oi japonica. 



