Further Studies on the Apogamy and Hybridization of the Hieracia. 2'57 



(most of the flowers of the head were taken away) and fertilized 

 the thus rightly castrated flower with the pollen of the father species. 

 This method, however, is so difficult and gives such small results, 

 as the delicate flowers are often destroyed in the operation, that a 

 patience and dexterity like Mendel's are required in order to employ it. 

 In the following I shall give the results of my crossing-experiments, 

 obtained since 1905, especially the results of the study of the later 

 generations of the first produced crosses, together with a report of 

 a new cross. 



/. H. pilosella x auranfiacum. 



In 1904 I had obtained a hybrid (No. 55) by crossing ff. pilosella 

 with H. aurantiacum. The single individual of this cross (represented 

 in the plate af the 1906 paper as fig. 7) did not fruit in 1905 after 

 isolation or castration, in contrast to both parents. But when the 

 heads were left to themselves during floweiing, a few full fruits were 

 developed, from which plants arose, different from one another and 

 to be considered as the result of new crosses caused by visits of 

 insects. Some of these were apparently pure H. pilosella and might be 

 supposed to be segregations, by back-crossing with the mother parent. 



The castration was repeated in 1906, 1907 and 1909, but always 

 with negative result. Isolation of some few heads was also tried, 

 but no fruit capable of germination was obtained in that way either. 

 The hybrid may thus be regarded as self-sterile. 



An experiment of crossing it with the pollen of the father plant 

 (H. aurantiacum) has until now given only a single individual as off- 

 spring; this was very much nearer to H. aurantiacum than was the 

 primary hybrid, but was still not a pure H. aurantiacum and was 

 also quite sterile'). 



2. //. aurivtda x aurantiacum. 



As before mentioned, H. auricula requires fertilization in order 

 to produce fruits capable of germinating, and it was therefore to be 



') An experiment with similar result has already been made by Mendel 

 (CoRRENS 190S. p. 245) by crossing the hybrid H. praealtum x aurantiacum 

 r= H. ma^yaricum x aurantiacum J with H. aurantiacum. He got as offspring: „zweierlei 

 Pflanzen, solche nämlich, welche mit der Bastard-Mutterpflanze ganz übereinstimmten, 

 und andere, welche dem H. aurantiacum um vieles näher standen." The former of 

 these categories is evidently apogamic F.,, while the latter corresponds to my 

 experiment. 



Induklivc Abslammungs- und Vtrerbungslchre. III. 1 7 



