— 235 — 



with a result, which agrees with Mur beck's, i. e. that the egg- 

 cell becomes an embryo. No doubt other botanists have made 

 experiments of the same kind, but I have not found more mentioned 

 in the literature 1 ). 



The results of the castration experiments may be 

 summed up thus: In the genus Hieracium we have apogamic and 

 non-apogamic species, together with transitions between both kinds; 

 the three subgenera are in this respect not quite alike, the subgenus 

 Stenotheca representing the most primitive stage with typical fertili- 

 sation; the subgenus Pilosella being intermediate, as it comprehends 

 both apogamic and typically fertilisating species, nevertheless mostly 

 apogamic; and the subgenus Archieracium representing the most 

 developed stage with nearly all species apogamic, only excepting 

 the H. umbellatum-group. The genus Taraxacum has gone a little 

 farther, as all its species are apogamic — as far as we at present 

 know. Corresponding to these results the cytologicai investigations, 

 which have been made, give a graduation in the abormal develop- 

 ment of the eggcell. The power to make hybrids in Pilosella and 

 Archieracium agrees well with the apogamic or non-apogamic 

 development, but still here much remains to be done in both sub- 

 genera and more too in the subgenus Stenotheca; the following 

 experiments with hybridisation in the subgenus Pilosella will, taken 

 together with the earlier experiments by F. Schultz, G. Mendel, 

 and A. Peter, throw some light upon several perplexing facts. 



III. Hybridisation Experiments. 



When I did my first crossing experiment by bringing the pollen 

 of H. aurantiacum to the stigmas of H. pilosella, I thought, it 

 would be of no result at all, as I had lately discovered the power 

 to set fruits after castration in the two species here in question. 

 Therefore in my first note in Ber. D. bot. Ges. (1904), p. 380 I 

 mentioned the experiment as one without any probability of success. 

 But a few months after (1904, 2) I could annonce (pp. 538 — 539), 

 that this very simple experiment had given rise to 19 individuals 

 of which one was an unquestionable hybrid, having characters 

 intermediate between those of the parents. 



x ) Perhaps I may here note, that I have tried castration with some other 

 Compositœ, but with negative results, viz. Calendula- and Dimorpho- 

 theca-sipecies, further Aster- and Eupatorium-speties from North-America. 



