Further Studies on the Apogamy and Hybridization of the Hieracia. 267 



1. It seems natural to place in one group H. pilose I la x anraji- 

 tiaciwi and H. exceilens x pilosella, consequently both combinations, 

 with H. pilosella as the one parent plant i). In this group the F^- 

 generation is (under isolation) wholly or nearly without power of forming 

 fruits capable of germination, — consequently self-sterile. By crossing 

 the Fl with one of the parents, an F2 of few individuals has been 

 produced which seems to segregate. 



2. Opposed to this stands the other group where Fj is rather 

 fertile by isolation and where F2 and Fg show full constancy. The 

 type of this group is H. exceilens x aurantiaaim; still perhaps No. 461 

 and the mutant of No. 463 belong to the first group. 



The hybrid H. auricula x auranfiacum must probably be divided 

 so that most individuals of Fi belong to the first group, while some 

 few belong to the second. 



The second group is of more interest, for here an experimental 

 proof is given that by hybridization between far distant 

 species within the subgenus Pilosella new forms can arise 

 which are fully constant and which behave as new species, 



III. 

 Apogamy and its Relation to Polymorphism. 



From the researches of MURBECK (1904), KIRCHNER (1905) and 

 especially from the cytological investigations of ROSENBERG (1906, 

 1907) on the apogamy of Hieraciiiin, it has been shown that the 

 development of the non-fertilized embryo goes on in different ways, 

 partly by true apogamy, partly by the curious apospory discovered 

 "by Rosenberg. We shall not enter into the cytology at great 

 length, but only mention that the embryo is always developed from 

 an "egg-cell" which has the vegetative (unreduced) number of chro- 

 mosomes; this form of apomixis is by H. Winkler (1908, p. 11) called 

 somatic parthenogenesis. Still, I prefer to maintain the termino- 

 logy of Strasburger (1904, p. 113 and p. 118), according to which 

 our case falls under apogamy, as we speak of parthenogenesis only in 

 the case where the egg-cell has the reduced number of chromosomes 

 and yet develops into an embryo without fertilization (H. Winkler's 



1) As regards the dimorphism of H. exceilens x pilosella. it is wortli recalling that 

 Mendel has produced a great number of hybrids between H. auricula (as mother) 

 and different races of H. pilosella, and that these hybrids of Fi have been like one 

 another (Correns 1905, p. 243). It seems thus that H. pilosella hybrids behave in a 

 different way from those in which H. aurantiaciim is fathi r jiareut. 



