336 University of California Puhlicalions in Agricultural Sciences [Vol. 2 



contains species with 7 or 14 pairs of cliromosomes, while Enamoria 

 and Galearia consist of species witli S or 16 pairs, except for T. 

 glomeraium which has 7 pairs; whereas Lagopus contains species Avith 

 7, 8 or a hirge number of pairs, possibly 4(S-49. Bleier presents some 

 evidence that differences in nuclear volume and in chromosome size 

 occur in the ^enus. The cases of Tri folium, Campanula, Lactuca, and 

 Crepis are alike in that, while many correspondences have been found 

 between chromosome number and classification, some exceptions still 

 exist which require further study. Even within Eucrepis, however, 

 Avhich shows a remarkable diversity of chromosome numbers, morpho- 

 lop:ical resemblances appear witliJn the section Avhich are correlated 

 with similarity of chromosome number and size. 



In the genus Senecio, Afzelius ('1924) reports a liijili degree of 

 homogeneity within the genus as indicated by close conformity to the 

 numerical series, 5, 10, 20, 30 ; also in most of the sections, as only one 

 of the eight sections contains species of different numerical rank. 

 However, as the species he has studied are mostly from the Old World, 

 the situation within the genus as a whole may yet be found to differ 

 considerably. 



In Carex, Heilborn (1924) has recently reported that species exist 

 with 9, 15, 16, 19, 24, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 40, 

 41, 42, and 56 as haploid numbers. Related species show some num- 

 erical similarity, although this is by no means so striking as in Lactuca. 



Crepis also contains a series of chromosome numbers like that 

 reported for Carex, 3, 4, 5, 6, 8, 9, and 20 pairs. Most of the species 

 with 3, 4, 5, 6, and 20 pairs have chromosomes similar in size, although 

 .some 4- and 5-paired species have chromosomes that are much larger 

 than is usual in Crepis, in so far as it has been studied cytologically. 

 Two of the three species which we have found with 8 and 9 pairs 

 have much smaller chromosomes than is usual in the genus. It was 

 noted above that the section Youngia might be removed from Crepis. 

 If this i^; done we shall lack species with 8 pairs. It is noteworthy 

 that Eucrepis contains species with 3, 4, 5, 6, and 20 pairs. Navashin 

 (1925/;) and Collins and Mann (1923) found evidence that polyploidy 

 occurs in Crepis, \)\\\ it was pointed out by Mann (1925) that some 

 other type of chromosome multif)lication must account for the origin 

 of most of the species which we have studied. Non-disjunction was 

 first suggested as a source of the chromosome differences observed by 

 Rosenberg (1918) ; and, whereas this cannot account for all the differ- 

 ences, it may be the most important factor. In any case it certainly 



