292 REPRODUCTION 



acters which exclude each other , or are opposed to each 

 other are concerned, each male or female reproductive cell 

 or gamete of the hybrid carries only one of the characters, 

 not both, i.e. each individual gamete of a cross bears either 

 the dominant or recessive character of the original parents, but 

 not both. 



Although the hybrid plant arising from the union of reproduc- 

 tive cells of, say, a pea, with round seeds, and one bearing wrinkled 

 seeds, contains both of these characters, even if both are not 

 visible, its reproductive cells carry only the round or the wrinkled 

 character in a pure state; its pollen-grains and ovules or the 

 generative nuclei in them, are either pure 'round' or pure 

 ' wrinkled.' 



Moreover, Mendel assumed that the number of male cells 

 (and female cells) bearing the ' round ' character was on an 

 average equal to those carrying the ' wrinkled ' character. 



Such assumptions being made, the result of the union when 

 only self-fertilisation is allowed will be understood from the 

 following : — 



A hybrid plant produced by the crossing of a parent bearing 

 round seeds (R) with one bearing wrinkled seeds (W) 

 possesses : — 



Male Gametes. Female Gametes. 



Some bearing the character R 



Any male gamete bearing the R (round) character has an 

 equal chance of meeting with a female gamete carrying R or W. 

 If it meets with R the plant produced will bear round seeds, and 

 will be quite pure (RR) in respect of this character of round- 



