ABSTRACT
The Hieracium hybrids were Gregor Johann Mendel's favourite children, but also those which brought him the greatest trouble, and those to which he gave most attention during the closing years of his experimental work. It was in the summer of 1866, after the publication of his first monograph, that he began these experiments in the hybridisation of Hieracium, a yellow-flowering composite resembling the dandelion, divided into the two subgenera Pilosella and Arch-hieracium. Mendel was unquestionably right in saying that the difficulties in the way of these experiments on Hieracium were considerable. The mere collection of material was arduous, for hawkweeds are not common in the neighbourhood of Brunn, and Arch-hieracium, in particular, is rare. The first crossing experiments with Hieracium, which Mendel made in the summer of 1866 when the Prussian invaders were billeted in the monastery, brought a positive result, though a small one.
