380 MODERN THEORIES OF HEREDITY. 



between " white " pollen and " yellow " flowers, we still find that 

 all the cross-bred seeds are ycllozv. We express this result 

 shortly by stating that yellow endosperm is " dominant " over 

 white endosperm, the latter being called " recessive." The 

 embryos contained in such seeds are hybrids of the first genera- 

 tion, and are described in the notation usually employed as Fl. 

 The hybrid seeds when sown produce healthy plants and flowers, 

 and if all the female flowers of such plants are pollinated with 

 ■' white "' pollen, we find approximately half the seeds produced 

 by them are yellow and half are white. ( The actual numbers 

 in an experiment were 26,792 yellow; 26,751 white.) It should 

 be noted that pollination with " white " pollen has different effects 

 on the hybrid yellow and the parent yellow The whites arc 

 found to breed true, but the yellows behave in the same manner 

 as the hybrids. 



Parents. White (pure; x Yellow (pure) 



F.I . Yellow (hybrid) x White (pure). 



Yellow (hybrid) 50%, White (pure) 50%. 



If instead of pollinating the hybrid yellow with " white " 

 pollen, we allow it to be self-pollinated, we find a still more 

 remarkable numerical relation between the offspring ( described 

 as F.2), namely, a proportion of three yellow seeds to one white 

 seed. (The actual numbers in an experiment were 16.592 

 yellow; 5,681 white.) Of these, all the white breed true, but 

 only one in three of the yellows, the remaining two-thirds giving 

 the same results as the F.^ hybrid. We may regard the colour 

 of the seeds as being due to the prisence or absence of a yellozv 

 pigment. 



Parents. Yellow (pure) x White (pure). 



F.L Yellow (hybrid) 



(self-pollinated). 



I 



F.2. 25% Yellow (pure) 50% Yellow (hybrid) 25% White (pure) 



(self-pollinated). (self-pollinated). (self-pollinated). 



F.3. All Yellow. 75% Yellow 25% White. All White. 



Other characters behave in tlie same way, e.g., starchv 

 (smooth seed) and sugary endosperm (wrinkled seed), starchy 



