24 PRINCIPLES OF BREEDING 



etc. He followed in detail the conduct of each character in 

 crosses derived from different forms, and the history of each 

 individual cross through several years of its growth. He 

 stated as a result that the gametes, 1 the egg-cells and pollen 

 grains, " are pure with respect to the characters they carry " : 

 in a cross between a smooth and a wrinkled pea the gametes 

 are either round or wrinkled, not blended. He found two dis- 

 tinct groups of characters, which he called Dominant and 

 Recessive, and he thought he could see the ratio in the 

 second growth of crosses (F 2 ) of three dominant (3/?) to one 

 recessive (i^). The first growth of a hybrid F v 



R. H. Bitten, M.A., Botanist, Agricultural Department, 

 Cambridge University, experimenting with wheat (1900-4), 

 confirms Mendel's views. He grouped pairs of unit characters 

 as follows, mostly shown in the second growth (F) of a cross, but 

 some seed characters not till the third growth, cross, or 

 generation (F 3 ). The following are examples : 



Dominant. 



Broad leaf. 



Hollow stem. 



Rough leaf. 



Red chaff. 



Red grain. 



Velvet or hairy chaff. 



Beardless. 



Hard grain. 



Susceptibility to rust. 



Keeled glumes. 



Recessive. 



Narrow leaf. 

 Solid or pith. 

 Smooth leaf. 

 White chaff. 

 White grain. 

 Glabrous chaff. 

 Bearded. 

 Soft grain. 

 Immunity from rust. 

 Rounded glumes. 



The self-pollinated second growth of cross wheats (F 2 

 generation) produces plants either beardless or bearded in very 

 nearly the ratio of $D to iR. Of the beardless or dominating 

 grains produced in F z generation, only J will produce the 

 purely beardless character, while produce both beardless 

 and bearded offspring in the proportion of 3 beardless to i 

 bearded. The recessive or bearded plants of the F 2 genera- 

 tion breed true. In 100 grains taken at hazard from the cross- 

 bred progeny F z , we do not find 75 pure dominants and 25 

 recessives ; but of the former only 25 are pure dominants 

 capable of breeding true to type, and 50 are similar to the 

 F 2 parent, and will, as F s , produce " the same type of offspring 



1 " Gamete, a protoplasmic body that unites or conjugates with another 

 to form a zygote." 



