SOME EXPEEIMENTS ON THE ORIGIN OF NEW 



FORMS IN THE GENUS HIERACIUM 



SUB-GENUS ARCHIE RACIUM. 



By C. H. OSTENFELD. 

 Landbohjjskolens Botaniske Institut, Copenhagen. 



(With Plates XVII and XVIII.) 



In earlier papers (1906, 1910, 1912) I have shown that within the 

 subgenus Pilosella of the genus Hieracium new forms arise by means 

 of hybridization associated with apogamy. That is to say : hybridization 

 produces the new forms (hybrids) and apogamy keeps them unaltered 

 from generation to generation. 



In the other big subgenus Archieracium of the same genus the 

 matter seems different. Most of the forms are purely apogamic and only 

 very few are sexual. Amongst the latter is H. unibellatum, and it is 

 interesting to know from Mendel's letters to Nageli, published by C 

 Correns (1905), that Mendel had succeeded, by using this species as 

 father, in producing two hybrids, the only ones produced experimentally 

 within Archieracium, at least as far as I am aware. As regards another 

 sexual Archieracium, H. virga aurea, I have observed that the offspring 

 from an individual which stood unprotected in my cultures showed 

 distinctly the influence of hybridization as it was very heterogeneous in 

 its appearance. 



With the exception of these few cases genuine hybrids amongst 

 Archieracium are not known, as we cannot rely upon the records of hybrids 

 given in floristic and systematic literature. Mendel complains that it is 

 " sehr schwiei'ig die Selbstbefruchtimg aufzuhalten " (according to our 

 present knowledge we have to replace the word "Selbstbefruchtimg" by 

 "apogamy"). All my own experiments have hitherto been fruitless. 



Meanwhile, as we find abundant polymorphism within this subgenus, 

 we must search for other explanations for it. The many forms — micro- 

 species we may call them — are apogamic and constant, the offspring 

 being like the parent. 



It seems quite natural to suppose that these microspecies are not 

 very old, nor all of the same age. Species of a wide geographical range 



8—2 



