210 THE SMALL GRAINS 



from the 800 F 2 hybrids will result 2000 more constant 

 awned plants and 6000 awnless, of which 2000 are con- 

 stant and 4000 are inconstant. 



219. Verbal expression of the law. Mendel's Law 

 may be expressed verbally as follows : Differentiating 

 characters in the parents of plant hybrids reappear pure 

 and in mathematical regularity in the second and suc- 

 ceeding generations of their progeny; each character 

 separates in each of these generations in one fourth of 

 the progeny, and remains constant thereafter. The 

 mathematical formula is, ID : 2DR : 1R. ID and 1R 

 come true, but 2DR breaks up again into dominants 

 and recessives in the ratio of 3 to 1. 



Mendel did his work with garden peas which are self- 

 fertile, and therefore the behavior of his hybrids was 

 similar to that of hybrids of the small cereals. He chose 

 a special set of parents to illustrate each character, one 

 set for seed shape, another for seed color, another for 

 pod shape. 



When the parents differ in two or more characters there 

 is effected a recombination of characters, of much value 

 in breeding. 



220. Unit-characters. From the work of Mendel, 

 De Vries, and others has resulted the conception of unit- 

 characters, so called because it is asserted that they may 

 be really treated as units of the plant under consideration. 

 These units are even regarded by Bateson (1909) as 

 corresponding in a sense with atoms in chemical elements. 



On this basis, all hybrids are defined as recombina- 

 tions of unit-characters of the two parents. No inter- 

 grading or modification of characters occurs. Extremes 

 are not resolved into means by crossing. Medium colors 

 of kernels in hybrids are explained by the fact of domi- 



