— 243 — 



the next summer comes, we shall learn much more about the 

 heredity of the second generation (the primary hybrids's offspring). 

 Owing to the very poor result of the sowing in July of 1905, the 

 progress of our knowledge has been very limited. In this year the 

 experiments are carried out on a larger scale. The perennial 

 Hieracia are unusually well fitted for studies of heredity, as it is 

 possible to get a new generation each year and at the same time 

 keep all the foregoing generations alive. 



If we sum up the hybridisation experiments hitherto 

 carried out by me, we get the following results: (1) A 

 hybrid, produced between H.pilosella as mother arid H. aurantiacum 

 as father, which is fairly intermediate between the parents. It has a 

 very reduced fruiting-power. While both parents give fruits after castra- 

 tion, this operation has hitherto not succeeded in the case of the 

 hybrid. Whether the hybrid is able at all to give any fruits on self-fer- 

 tilisation, is not yet decided. Fruits collected from not-isolated flowers 

 have given an offspring of which the individuals are heterogeneous and 

 mostly nearer to H. pilosella, than the primary hybrid is. It is 

 not impossible that these fruits have come from flowers crossed 

 with H. pilosella which grows in the neighbourhood of the hybrid. 

 Mendel (1870, p. 51 & p. 53, and by G. Gorrens 1905, p. 233 etc.) 

 points out again and again, that the offspring of Hier acium-hy hvids, 

 when arisen from "self-fertilized" flowers, always are alike and do 

 not split as the offspring of Pis um-hybrids do. I think, he is quite 

 right in his statement, and the cause of this constancy is the apogamy ; 

 if so, the heterogeneous offspring of the here mentioned hybrid is 

 due to the supposed crossing with the mother-species. In each 

 flower-head of the hybrid only very few fruits are full, the main 

 part being empty (barren); but unfortunately I have no figures 

 from which to determine the percentage of the full fruits. Further 

 investigations will clear up this question. 



(2) The species H. excellens, of which the pollen is aborted in 

 all the flowers and which consequently is female, gives fruits after 

 castration or isolation, and is of course apogamic; but not all the 

 flowers develop full fruits. [ did not examine this phenomenon 

 precisely in the true flowering-season (June — July), but I remember 

 with certainty that I always found some barren fruits among the 

 full ones. In autumn I counted the proportions between apparently 

 full and barren fruits of some corymbs. It then appeared, that 

 about half the fruits were barren, as will be seen from the following 



)()* 



