2^6 Ostenfeld. 



IV. 



The Importance of Hybridization for the Origin of New Species, with 

 special regard to Hieracium. 



It would far exceed the scope of the present paper to give a 

 full account of the question about the importance of hybridization 

 for the origin of species. Much has been said pro et contra in this 

 matter, which in the last decennium has entered upon a quite new 

 phase by the general acknowledgment of the fundamental importance 

 of the Mendelian segregation, both in the animal and the vege- 

 table kingdom. 



In the following pages I restrict myself to some remarks — with 

 the Hieracia as starting point — on the question what views are now 

 applicable to this interesting and important matter. 



We find the only detailed remarks on the importance of the 

 Hieracium hybrids for the origin af new forms in the monumental 

 work by C. von N.\GELI and A. Peter on the Piloselloideae of 

 Central Europa (1885) and in the detailed paper by A. Peter 

 on the hybrids of the Piloselloideae (1884). A most remarkable 

 thing, regarding our question, in these papers is to see how little 

 these authors have understood the value of Mexdel's experimental 

 researches, and this seems still more extraordinary when we think 

 of the letters from Mendel to N-^GEi.i, published posthumously by 

 Correns (1905), letters which have so often been quoted in the pre- 

 ceding pages and which contain much more copious information on 

 Hieracium hybrids than Mexdel's own short account of 1870. The 

 importance of Mendel's researches has evidently not become clear 

 to the eminent botanist NAgelI; nor to W. O. FocKE, who in his 

 meritorious book "Die Pflanzenmischlinge" (1881) onl3' briefly enume- 

 rates the hybrids published by Mendel (1870), and, later on, 

 incidentally mentions Hieracium as an exception from one of his rules 

 ("Sätze"), viz.: that all individuals of the first hybrid generation are 

 "einander in der Regel völlig gleich" (1. c, p. 469). 



The papers of NAgeli and Peter, mentioned above treat only 

 of the subgenus Pilosella. The authors point out that by hybridization 

 is "im allgemeinen keine neue Erscheinung hervorgebracht, weil die 

 Bastarde lediglich eine Mischung der elterlichen Merkmale repräsen- 

 tieren" (^885, p. 63). The heterogeneity of the first hybrid generation 

 (Fl) is well known to them, and they even give an explanation of it, viz. : 



