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



It is evident that, generally speaking, there is a definite correspond- 

 ence between the taxonomic position of the species studied and their 

 chromosome number and especially with chromosome size, and that the 

 new taxonomic grouping increases this correspondence. It is almost 

 perfect in Section II, and in Section III (cf. table 3), and the species 

 that stand apart in the classification also differ markedly from the rest 

 in either size or number of chromosomes (Sections V, VI, and VII). 

 It will be noted that Section III and Section VI contain species 

 with .^imilar chromosome numbers and sizes, parviflora and setoaa 

 having very similar size differences, as do also taraxacifolia and 

 tectorum. It would seem worth while to test these groups by means 

 of species-hybridization. Sections VII and VIII as compared with 

 Sections V and X exhibit the most extreme differences in chromosome 

 size. 



LITERATURE AND DISCUSSION 



The numerous summaries of chromosome numbers which have 

 appeared in recent years clearly indicate that there is some parallelism 

 between chromosome number, size, and shape and relationship in the 

 plant and animal kingdoms. In general, members of the same genus 

 usually have similar chromosome numbers. In the Liliaceae, for 

 instance, each genus has a characteristic number of chromosomes. On 

 the other hand, in wheat, instead of exact numerical correspondence 

 within the genus, the species fall into three groups with respect to 

 chromosome number (Sakamura, 1918), einkorn having 7, emmer 14, 

 and vulgare 21 pairs of chromosomes. These groups also differ from 

 one another in susceptibility to rust, serological relations, and 

 morphology (Sax, 1921). Thus in the genus Triticum the most similar 

 species are most alike in chromosome number. Winge (1917, ])p. 166- 

 168) cites an interesting case from the Compositae, Species were 

 described as having 8, 9, 14, 16, 18, 24, 27, 32, 36, and 45 pairs. When 

 these species were classified by tribes, the numbers formed two series 

 with 8 as the ground number for the Heliantheae, and 9 for the 

 Anthemideae. Marchal (1920) recently noted that the species of the 

 genus Campanula which belong to the section Medium have N values 

 of 17, 34, or 51, but finds that the other section of the genus fails to 

 show a similar numerical seriation, including such N values as 8, 10, 

 and 13. He suggests (p. 66) that "The results of the cytological study 

 of species of section II [Rapunculus] tend to show that this grouping 

 is much less natural and less homogeneous than the preceding. ' ' 



