CASTRATION AND HYBRIDISATION IN THE GENUS HIERACIUM. 285 
CASTRATION AND HYBRIDISATION IN THE 
GENUS HIEHRACIOM. 
By C. H. Ostenrexp, of Copenhagen. 
I HAVE the pleasure of submitting to you a short report on my experi- 
ments in castration and hybridisation with some species of Hieraciwm. 
The experiments are not of any great importance from a practical point 
of view, but they are of no small scientific and theoretical interest, as the 
phenomena with regard to fertilisation and fructification in the Hieracia 
are very strange. 
In the beginning I worked in conjunction with Dr. Raunkiaer, of 
Copenhagen, and we succeeded in proving that a great many species of 
Hieracium develop fruits without fertilisation, a phenomenon which is 
generally called parthenogenesis or apogamy. In 1902 Dr. Raunkiaer 
proved the same to be the case with all the forms of Taraxacum 
(dandelion) hitherto examined : and as it occurred also in the Hieracium 
species first examined, the fact suggested a doubt whether the numerous 
Hieracium forms mentioned and described as intermediate forms really 
were hybrids, which they most often are said to be. Nevertheless the 
doubt was not correct ; some species of the genus readily produce hybrids. 
Mendel published in 1870 a short note on Hieraciwm hybrids produced by 
him ; and lately Correns has published the letters from Mendel to Nigeli, 
in which we get a much fuller report of the great work of Mendel than in 
his own little paper. He succeeded in crossing a good many species of the 
sub-genus Pilosella and got a large number of hybrids; but there is a 
great difference with regard to the readiness of each species to produce 
hybrids. His experiments with species of the other sub-genus Archiera- 
cium had no result, with the exception of two hybrids both having H. 
umbellatum as father. Unfortunately, he does not tell us more about the 
last hybrids, which are of special interest, as they are the only ones of the 
Archieracia hitherto produced. 
Besides Mendel, A. Peter, together with Niigeli, studied Hieraciwm 
hybrids extensively, but he has not done much by experimental methods. 
It is perhaps worth noticing that the first botanist who crossed 
Mieracium species with positive results is F. Schultz; he had already in 
1856 published a little note about this. It is rather curious that we do 
not find other publications about the artificial hybridisation of Hieracia, 
and that the last fifteen to twenty years do not show any progress in that 
direction. 
Before reporting my own experiments, I wish to say that at an early. 
stage of my studies the apparent contrast between apogamy and hybridisa- 
tion necessarily required cytological examinations of the egg-cell develop- 
ment; but, not being acquainted with the modern technique and methods, 
I myself was unable to do this, and I was very glad when Dr. Rosenberg, 
of Stockholm, accepted my proposal to do the cytological researches. 
