298 Universitu of CdJifoniia Puhlicdiidtis in .ifirioilfiiriil Sciences [Vol. _ 



concluded that the four-pair species have arisen from a three-pair species 

 by the fusion of two gametes each of which has received an extra short 

 chromosome. Although he did not publish measurements on the two 

 five-pair species which he studied (rubra and multicaulis) , he believed 

 that both have three of the short chromosomes, and that these types 

 have originated by a repetition of the process which gave rise to the 

 four-pair types. In his 1920 contribution he changes his count in biennis 

 from twenty to twenty-one pairs and conclucies that it represents the 

 three chromosomes of capillaris multiplied fourteen times. 



Marchal, whose work was done without knowledge of Rosenberg's 

 paper, expressed (1920) the belief that four is the ground number of the 

 genus Crepis. He noted that p.m.c. of a slightly aberrant capillaris plant 

 had what appeared to be a large quadrivalent multiple chromosome 

 plus two smaller but equal elements, and that most of the species of 

 Crepis seemed to have four pairs of chromosomes. He therefore con- 

 cluded that capillaris had arisen from the type by end-to-end union 

 between two chromosomes. He believed that the differences in length 

 which had been noted for C. lanceolata platyphylla (Tahara and Ishikawa, 

 1911) could be accounted for by bipartition of one chromosome of a 

 species with four pairs. He further suggested that six-pair species 

 might arise by doubling of the three, and an eight-pair species by 

 doubling of the four. He counted sixteen pairs for biennis and noted 

 that, while the individual chromosomes in the p.m.c. of this species 

 appeared somewhat smaller than those of certain four-chromosome 

 species, the total mass was much greater. He then concluded that 

 biennis is an eight-ploid species. 



MATERIAL AND METHODS 



A large numl^er of species of the genus Crepis have been grown and 

 identified in the greenhouse of the Division of Genetics of the University 

 of California by Professor E. B. Babcock, thus making it possible to be 

 certain of the specific determination of the material which was studied 

 cytologically. Since the chromosome numbers which have been found 

 to characterize the species thus identified differ in several instances from 

 previously published counts, the data ai'e presented in a convenient 

 form in ta})le 1. The root tips were fixed in chrom-acetic-urea and 

 stained in Heidenhain's iron-haematoxylin. In most species the reduced 

 number has also been counted by Boiling's iron-aceto-carmine method. 



