358 EXPERIMENTAL STUDY OF INHERITANCE 



blue seeds, one character of each parent being dominant, and 

 one character of each parent being recessive. The hybrids were 

 inbred, and the progeny (F 2 ) showed four combinations — smooth 

 blue, smooth white, wrinkled blue, and wrinkled white (the 

 dominant characters are italicised). 



In the next generation (F 3 ), the wrinkled white, inbred, yielded 

 wrinkled white — a case of extracted recessives breeding true. 

 The smooth whites and wrinkled blues, inbred, yielded partly 

 forms like themselves and partly wrinkled white. The smooth 

 blues, inbred, yielded the same combinations as in F 2 . 



A finer corroboration of Mendelism could hardly be wished. 



Nettles. — Correns crossed two " species " of stinging-nettle, 

 Urlica pilulifera L. and U. dodartii L., which resemble one 

 another except as regards leaf-margin, strongly dentate in the 

 former, almost entire in the latter. The hybrid offspring (F 1 ) 

 have all dentate leaves like the male or the female parent, as 

 the case may be. The dentate character is absolutely dominant. 

 The inbred '(self-fertilised) hybrids produce offspring (F 2 ) of two 

 kinds, with dentate and with entire margins, on an average in 

 the Mendelian proportion, 3:1. 



Immunity to Rust in Wheat. — Some kinds of wheat are very 

 susceptible to the fungoid disease known as " rust " ; others 

 are immune. The quality of immunity to rust is recessive 

 to the quality of predisposition to rust. 



" When an immune and a non-immune strain are crossed 

 together the resulting hybrids are all susceptible to ' rust.' 

 On self-fertilisation such hybrids produce seed from which 

 appear dominant ' rusts ' and recessive immune plants in the 

 expected r^tio of 3 : 1. From this simple experiment the 

 phrase ' resistance to disease ' has acquired a more precise 

 significance, and the wide field of research here opened up in 

 this connection promises results of the utmost practical as well 

 as theoretical importance. To the question, ' Who can bring 

 a clean thing out of an unclean ? ' we are beginning to find an 



