Defective inheritance-ratios in Bursa hybrids. 



By Dr. George Harrison Shull, 



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



New York. 



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 bas 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 Heeger 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 : *) 



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" 7 and a more or less rounded or 



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

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

 August 19—24 1907. „Advanced reprint" issued in 1910. 



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

 57 pp., 23 text^figs., 4 pls., Publ. No. 112, Carnegie Institution of 

 Washington, 1909. 



