BLASTOGENIC VARIATIONS. 157 



sequent generations proved themselves to be pure domi- 

 nant forms, whilst two thirds of them still retained 

 their hybrid nature, as was shown by their yielding, in 

 the next generation, recessive and dominant forms in 

 the proportion of 1:3. The gradual resolution of the 

 original hybrid forms into pure parental forms may be 

 represented diagrammatically thus,* it being assumed 

 that 64 hybrids with yellow cotyledons had been pro- 

 duced by the crossing of parental forms having respect- 

 ively green and yellow cotyledons. 



Parents I. Gen. II. Gen. III. Gen. IV. Gen. V. Gen. 



green 



yellow . 



64 yellow 



T 



16 green 16 green 16 green 16 green 



8 green 8 green 



f 8 green [ 4 green 4 green 



( 2 green 



32 yellow -( ( 16 yellow | ( 8 yellow < 4 yellow (hy.) 



A [l2-{ 1 2 yellow 



( 8 yellow ( 4 yellow 4 yellow 



8 yellow 8 yellow 



16 yellow 16 yellow 16 yellow 16 yellow 



We see that of the plants produced by crossing the 

 original 64 yellow hybrids haphazard amongst them- 

 selves, a quarter are of the pure green form, a quarter 

 of the pure yellow form, and a half of them hybrids 

 with the yellow character dominating. On crossing 

 these hybrids among themselves, we see that in each 

 subsequent generation their number is reduced by half, 

 till in the seventh generation only 1 of the original 64 

 hybrids would be still remaining. 



The explanation of this result was clearly laid down 

 by Mendel, he supposing that the cross-bred plant pro- 

 duced pollen grains and ovules, each of which bore only 

 one of the alternative varietal characters, and not both. 

 If D and E represent the two characters present in dif- 



* Modified from Correns (Ber. d. deutsch. bot. Gesell., xvii. 

 p. 162, 1900. 



