22 E. B. Babcoc\ 



its support. However, if both genera originated in south-central 

 Asia and migrated into North America by way of a land bridge, 

 even though Crepis is the more primitive, a difference in time 

 of migration and the special adaptations of Hieracium species 

 for rapid dissemination would explain the present distributional 

 relations of the two genera. Furthermore, the South American 

 species of Hieracium having attenuate achenes and fine white 

 pappus must be among the most advanced members of the 

 genus. It is well known that various species of flowering plants 

 in South America are closely allied to North American species 

 and appear to have migrated from north to south. 



Lactuca (fig. 2) has a distributional range about as extensive 

 as that of Crepis but, in certain morphological features, particu- 

 larly in specialization of fruits, it appears to be a more advanced 

 group of species. Its extensive geographic range does not neces- 

 sarily indicate antiquity greater than that of Crepis. 



Prenanthes is less extensive in distributional range than Lac- 

 tuca (fig. 2), but the evidence from comparative morphology 

 shows that Prenanthes is the more primitive. If the distribution 

 of Prenanthes be examined in some detail, it will be found to be 

 consistent with the conception that it was formerly more wide- 

 spread. However, the small areas indicated on the map (fig. 2) 

 in the Canary Islands, Java, South America, and probably Soco- 

 tra Island may be disregarded. Herbarium studies made since 

 this map was printed indicate that none of these species are of 

 this genus. Nevertheless, both comparative morphology and dis- 

 tribution indicate that Prenanthes may be more primitive than 



Crepis. 



The Genus Crepis 



The genus comprises three subgenera, Catonia, Eua-epis, and 

 Bar/{hausia, which are differentiated primarily according to de- 



