MENDEL'S DISCOVERIES 541 



spect to tallness and dwarfness and tho facts carefully recorded. 

 The individuals of the F^ generation were allowed to self-ferti- 

 lize, and from the seeds obtained the Fz generation was grown, 

 and the individuals in this generation were studied in the same 

 careful wixy as those of the previous generations. Throughout 

 a number of generations the behavior of tallness and dwarfness 

 was carefully recorded. In this way he studied many pairs of 

 characters such as: (1) shape of pod (whether simply inflated 

 or deeply constricted between the seeds); (2) color of unripe 

 pod (whether green or yellow); (3) distribution of flowers on 

 the stem (whether distributed along the axis of the plant or 

 bunched at the top); (4) color of cotyledons (whether yellow 

 or green); (5) shape of seeds (whether round or wrinkled); 

 and (6) color of seed coat (whether gray or brown, with or 

 without violet spots, or white). 



Mendel's Discoveries. — Mendel found that in most cases the 

 different pairs of characters investigated behaved in the same 

 way and appeared in a regular way in the successive generations. 

 Furthermore, it made no difference as to which variety was used 

 as the mother parent. In case of tallness and dwarfness, all the 

 plants of the first or Fi generation were tall. They were all like 

 the tall parent. In the second or F2 generation there were both 

 tall and dwarf plants, but there were three times as many tall 

 plants as dwarf ones, the tails and the dwarfs thus occurring 

 in the ratio of 3 : 1 . The offspring of the dwarfs were all dwarfs 

 in the third or F^ generation and in all' succeeding generations. 

 The dwarfs, therefore, were pure for dwarfness, that is, they 

 had no factors or genes for tallness in them. One out of every 

 three tall plants also bred true and, therefore, proved to be 

 pure for tallness, but two out of every three tall ones gave three 

 times as many tall ones as dwarfs or a ratio of 3 : 1, thus being 

 apparently the same in constitution as each of the individuals of 

 the Fi generation. They evidently contained factors or genes 

 for both tallness and dwarfness. The dwarfs and one-third of 

 the tall ones of the 7^3 progeny bred true, while two-thirds of 

 the tall ones again bred as in the previous generation, giving the 

 ratio 3:1, and two-thirds of the tall ones being impure. This 

 proved to be a constant way of behaving throughout genera- 

 tions. The character of the individuals of the different gen- 

 erations are shown in Figure 1^.75. Thus by the further breed- 



