Variation and Heredity 279 



Mendel's experiments are concerned. The flower of the pea 

 is especially suitable for experiments of this kind. It cannot 

 be accidentally fertilized by foreign pollen, because the repro- 

 ductive organs are inclosed in the keel of the flower, and, as 

 a rule, the anthers burst and cover the stigma of the same 

 flower with its own pollen before the flower opens. In order 

 to cross-fertilize the plants it is necessary to open the young 

 buds before the anthers are mature and carefully remove all 

 the anthers. Foreign pollen may be then, or later, introduced. 



The principle involved in Mendel's law may be first stated 

 in a theoretical case, from which a certain complication that 

 appears in the actual results may be removed. 



If A represent a variety having a certain character, and 

 B another variety in which the same character is different, 

 let us say in color, and if these two individuals, one of each 

 kind, are crossed, the hybrid may be represented by H. If 

 a number of these hybrids are bred together, their descendants 

 will be of three kinds; some will be like the grandparent, 

 A, in regard to the special character that we are following, 

 some will be like the other grandparent, B, and others will be 

 like the hybrid parent, H. Moreover, there will be twice as 

 many with the character H, as with A, or with B. 



A B 



\/ 



H 



\ 



A 



\ 

 B 



/ H \ 



A 



A 



\ B 



\ 

 B 



/ A \ 



A / 



A 



B 



\ 



B 



H 



If now we proceed to let these As breed together, it will 

 be found that their descendants are all A, forever. If the 



