CEREAL IMPROVEMENT HYBRIDIZATION 209 



ment of Mendel's views in connection with those of De 

 Vries on " mutations " and " elementary species " and of 

 Johannsen on pure-line selection has effected recent plant- 

 breeding discussion and practice to an extent that is 

 revolutionary. 



218. Explanation of the theory. The theory of Men- 

 del, known generally in recent years as " Mendel's Law," 

 may be explained as follows : Suppose that in 1915, 

 16 flowers of a Fultz wheat plant having awnless spikes 

 are successfully fertilized with pollen from a Turkey 

 wheat plant having awned spikes. The 16 kernels re- 

 sulting, when planted next year, will produce 16 new 

 hybrid plants, all of which will be awnless or slightly 

 awned. Absence of awns is therefore said to be domi- 

 nant. This is the first generation, indicated in technical 

 literature as FI. If 100 kernels from each of these 

 plants are planted in 1917, the 1600 plants of the F 2 , or 

 second generation produced, will segregate, as to the 

 character of awns, into three groups, of (1) 400 plants 

 with awned spikes, (2) 400 plants with awnless spikes, 

 and (3) 800 plants that are true hybrids ; but as absence 

 of awns is dominant these hybrids will also be awnless 

 or some of them slightly awned. Practically, therefore, 

 there are, in appearance, 2 groups resulting, one of 400 

 constant awned, and another of 1200 all awnless, but 

 theoretically one third of the latter are constant awn- 

 less and two thirds are inconstant awnless. The progeny 

 of the 400 awned plants remain constantly awned through 

 all succeeding generations, and the presence of awns is 

 therefore known as a recessive character. If 10 kernels 

 from each plant are again planted in 1918, there will 

 result the third or F 3 generation, in which 4000 plants 

 are constant awned and 4000 constant awnless, while 



