Origin of Species in the Genus Hieracium. 
347 
EXPERIMENTS ON THE ORIGIN OF SPECIES IN THE 
GENUS HIERACIUM (APOGAMY AND HYBRIDISM) 1 . 
By C. H. Ostenfeld (Copenhagen). 
I. 
S is well known, Hieracium is a very polymorphous genus. 
Specialists have been able to distinguish numerous minor 
species (“ petites especes ”) or separable forms which nevertheless 
stand so near to each other that a botanist not familiar with the 
genus hardly distinguishes one from another. In Scandinavia for 
instance Dr. Dahlstedt and his pupils have distinguished many 
hundreds of such species in the sub-genus Archieracium alone, and 
in the British Isles the number of minor species is also fairly large. 
During several years (since 1903) I have studied this interesting 
genus in order to find out the causes of this polymorphy, or at 
least to trace facts which stand in relation to it, and I think that I 
have found such facts in the apogamy and hybridism which occur 
in the genus. 
In 1903 Raunkiaer and I proved that many species are apoga- 
mous, i.e., that they produce fertile seeds without fertilisation. 
Earlier than that Raunkiaer had shown that the species of Taraxacum 
are apogamous. His method is very simple : he cuts off with a 
razor the upper part of unopened flower-heads, thus removing 
both the anthers and the stigmas; heads treated in this way— 
“castrated”—grow out and give fertile seeds, obviously without any 
fertilisation. The same method has been applied by us to the 
Hieracia and with the same effect, as regards many, but not all 
species. 
It was thus shown that many Hieracia are apogamous, but no 
information was found relating to the details of the apogamy. 
Cytological studies by S. Murbeck and O. Rosenberg have cleared 
the matter up. I shall not enter into details on this point, which may 
be found in the papers published by these authors; it will be 
sufficient to say that, in some cases, the mother-cell of the 
embryo-sac grows out to form an apogamous embryo-sac, whilst in 
other cases a cell from the nucellus is transformed into an apo¬ 
gamous embryo-sac. In both cases this embryo sac has the 
1 Read before the Botanical Section of the “ British Association” 
at Dundee, September, 1912. 
