i68 MENDELISM 



a yellow strain the grains are yellow. On the other 

 hand, the grains upon a plant belonging to a yellow 

 strain retain their yellow colour even if the flowers 

 which produce them have been pollinated from a white 

 variety. 



These facts are expressed in technical language by 

 saying that yellowness is dominant over whiteness, and 

 the latter is said to be recessive. 



Let us now suppose that we have sown a number 

 of the yellow grains derived from the cross yellow x 

 white* or white x yellow, and that we have exposed 

 the female flowers of the resulting plants at the proper 

 stage of their existence to the influence of pollen 

 derived from a pure white strain, taking care that 

 none of their own hybrid pollen falls upon them at 

 the same time. The result of this experiment takes 

 us at once to the very heart of the Mendelian theory. 

 Half the total number of grains obtained in this way 

 from the cross (white x yellow) x white are white, 

 and half are yellow. 



Thus in an experiment carried out in the manner 

 described there were obtained upon ninety-five plants : 



Yellow grains 26,792, or 50*03 per cent. 

 White grains 26,75 1, 49-97 



But we must go further than this. On sowing the 

 white grains obtained in this second generation (F 2 ), 

 and allowing the plants obtained from them mutually 

 to pollinate one another, cobs were obtained bearing 

 exclusively white grains without any trace of yellow- 

 ness. 



* x is to be read ' fertilized with pollen from.' 



