SEGREGATION AND DOMINANCE 125 



the two gametes which uniting produce a zygote 

 that develops into the seed and subsequently into 

 the adult plant of the next generation. In artifi- 

 cially crossing normally self-fertilized flowers it is 

 necessary to carefully remove the stamens from one 

 flower while its pollen is still immature, and later, at 

 the proper time, to transfer to it ripe pollen from 

 another flower. 



Mendel's cross-breeding experiments on peas 

 showed certain numerical relations which gave rise 

 to what has come to be rather indefinitely known as 

 "Mendel's law." This law may be temporarily 

 formulated as follows : — 



When parents that are unlike with respect to any 

 character are crossed, the progeny of the first gen- 

 eration will apparently be like one of the parents 

 w4th respect to the character in question. The 

 parent which impresses its character upon the off- 

 spring in this manner is called the dominant. When, 

 however, the hybrid offspring of this first generation 

 are in turn crossed with each other, they will produce 

 a mixed progeny, 25 per cent of which will be like the 

 dominant grandparent, 25 per cent like the other 

 grandparent, and 50 per cent like the parents resem- 

 bling the dominant grandparent. 



An illustration will serve to make plain the man- 

 ner in which this law works out. 



Mendel found that when peas of a tall variety 

 were artificially crossed with those of a dwarf variety, 

 all the resulting offspring were tall like the first 

 parent. It made no difference which parent was 



