The Origin of Crepis and Related Genera 21 



range of the presumably parental species. In fact, the distri- 

 bution of Zwischenarten far beyond the range of one or both 

 parents has been frequently observed. Although many of these 

 intermediate species are doubtless hybrids, their distributional 

 dominance is easily explained by the high frequency of apomic- 

 tic reproduction in this genus. Predominance of interspecific 

 hybrids has been observed in many other genera, but in Hiera- 

 cium it has been an important factor in bringing about the 

 wide distribution of the genus. Undoubtedly another impor- 

 tant factor is the usually small size of the achenes, which makes 

 them especially well adapted for wind distribution. In Crepis, 

 on the contrary, the fruits of many species, especially the more 

 primitive ones, are larger and heavier and apomixis is almost 

 unknown. Yet the distribution of Crepis is nearly as extensive 

 as that of Hier actum, the chief diflference being that Hieracium 

 occupies South America whereas Crepis is not known to occur 

 south of northern Mexico. But Crepis, even after certain species 

 are excluded, includes some of the most primitive types in the 

 Crepidinae (e.g., C. pontana and C. sibirica). Furthermore, 

 Crepis is more widely distributed in Africa than is Hieracium. 

 Hence it is probable that Crepis represents a progenial stock 

 from which both these genera were derived. 



The wide distribution of Hieracium in South America and 

 the complete absence of Crepis from that continent present a 

 distributional problem calling for more detailed study. A sug- 

 gestion worth considering is that distributional relations such 

 as these will eventually be found to have a bearing on the con- 

 cept of continental displacement. Good" states that, although 

 there is no satisfactory hypothesis of continental displacement, 

 it is believed that one will be forthcoming and that the geog- 

 raphy of the flowering plants will afiFord important evidence in 



