Son 
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 heredily, 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 and 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 C. Correns 1905, p. 233 etc.) 
points out again and again, that the offspring of Hieracium-hybrids, 
when arisen from “self-fertilized” flowers, always are alike and do 
not split as the offspring of Pisum-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 
16* 
