18 MENDELISM 



pure in respect of each character,' could not be better 

 shown." 1 



In the following diagram the black circles represent 

 the black andalusians, the white circles the white birds, 

 and the dotted ones the blue birds. 



0X0 



I I i I 

 • X • © oxo 



X o 



So far we have been considering Mendel's study of a 

 single pair of contrasted characters, but he also observed 

 the results of crossing plants which exhibited two pairs. 



He called this " di-hybridism," or double-hybridism. 

 For instance, he studied height and colour in the same 

 hybrids by crossing a tall pea bearing coloured flowers 

 with a dwarf white. Here you have two plants contrasted 

 as to size and also as to the colour of the flowers. Of 

 course the results are more complicated than when a single 

 character only is dealt with. He found that each character 

 acts independently, for tallness and colour are always 

 dominant to dwarfness and absence of colour. You can 

 therefore tell me what will be the result of — 



Tall coloured x Dwarf white. 



The Fj generation will all be tall coloured. 



The Fij generation will follow the result already 

 established (Law 6) and consist of coloured plants and white 

 in the proportion of 3 to I, and tails to dwarfs in the 

 proportion of 3 to 1. The smallest number of plants in 



1 The wording of the above quotation has been slightly altered so as 

 to avoid technical terms. 



