Defective inheritance-ratios in Bursa hybrids. 



By Dr. George Harrison Shull, 



Station for Experimental Evolution, Cold Spring Harbor, Long Island, 



New York. 



(Sonderabdruck aus dcm XLIX. Bande der Verhandlungeu des naturforschenden Vcreiues iu Briinn.) 



Several years ago (1905 1907) I was making extensive 

 cultures of Bursa (Capsella) bursa-pastoris, of Bursa Heegeri, and 

 of hybrids between these two species. Bursa Heegeri is generally 

 conceded to have originated from B. bursa-pastoris by a recent 

 mutation and has been found in nature only once in a situation 

 which would warrant the belief that it had not been derived 

 from a near - by experimental culture. Although a number of 

 specimens were found by Professor H e e g e r at the original locality 

 on the market-place at Landau, Germany, in 1897, so far as is 

 now known these represented a single elementary form or biotype . 

 Bursa bursa-pastoris } on the other hand ; is of almost world- wide 

 distribution, and presents an unknown number, but certainly a 

 large number, of distinct biotypes. 



In my cultures of the latter species I found four forms of 

 rosette which were related to one another as the four terms of 

 a Mendelian di-hybrid. These four biotypes were named and 

 described as follows : J ) 



Type (a). Bursa bursa-pastoris heteris has the leaves divided 

 to the mid-rib, the terminal lobe being usually separated from 

 the nearest lateral lobes by clean, deep incisions. The lateral 

 lobes consist essentially of two features, an elongated proximal 

 portion, the primary lobe", and a more or less rounded or 



*) n Results of crossing Bursa bursa-pastoris and Bursa Heegeri". 

 6 pp. Proceedings Seventh International Zoological Congress, Boston Meeting, 

 August 1924 1907. Advanced reprint" issued in 1910. 



n Bursa bursa-pastoris and Bursa Heegeri: Biotypes and hybrids". 

 57 pp., 23 text-figs., 4 pis., Publ. No. 112, Carnegie Institution of 

 Washington, 1909. 



des naturf. Vereines in Bruon. XLIX. Band. * 





