1 6 E. B. Babcoc\ 



and beakless, with lo fine, rounded ribs. In fact, both involucre 

 and fruits are more Hke Crepis than Ixeris. The other genus, 

 Paraixeris, also resembles Ixeris somewhat, but differs in having 

 the stem much branched, the fruiting heads nodding, and the 

 achenes subcompressed with 14 or 15 narrow, rounded ribs and 

 a short coarse beak. Nakai's contention that these two genera 

 are intermediate between Crepis and Lactuca may be well 

 founded, but in my opinion they are both nearer to Crepis than 

 to Ixeris and, as will be shown below, their chromosome num- 

 ber supports this view. At the same time the relations of these 

 two small genera to Prenanthes should be investigated, particu- 

 larly since in both there is a strong habital resemblance to this 

 genus. 



We turn now to the cytological evidence. Although the data 

 on chromosome numbers are far from complete, yet something 

 is known about most of these related genera. At present, the 

 basic haploid numbers as known in the four larger genera are: 

 Hieracium, 9; Lactuca, 8, 9; Taraxacum, 8; Prenanthes, 9, 8; 

 and in the smaller genera under discussion the numbers are: 

 Crepidiastrum, 5; Paraixeris, 5; Chondrilla, 5; Ixeris, %\ Youngia, 

 8; Paleya, 8; Aetheorrhiza, 9. In Crepis, after the exclusion of 

 those species which on morphological grounds belong in other 

 genera, the numbers 8 and 9 do not occur as basic haploid num- 

 bers, whereas 5 is a basic number. This indicates a closer relation 

 between Crepidiastrum, Paraixeris, and Crepis than between 

 Crepis and the other excluded genera. Furthermore, all the 

 species of Ixeris, Youngia, and Aetheorrhiza thus far examined 

 have chromosomes which are definitely smaller than those of 

 most species of Crepis. 



Thus the chromosomes provide important evidence in sup- 

 port of the delimitation of Crepis as oudined above. Cytology 



