322 HEREDITY 



will produce plants which will bear flowers of three colors. 

 Of every 1000 blossoms, approximately 250 will be red, 250 will 

 be white, and 500 will be pink. The colors will be in the proportion 

 of 1 : 1 : 2. The various colors of the four-o'clocks of succeeding gen- 

 erations will vary in the same way as those of the Andalusian fowl. 



Experiments in plant breeding. Long before the foregoing 

 experiments were carried on, Gregor Johann Mendel (1822-1884), 

 an Austrian priest and head of a monastery, was especially inter- 

 ested in cultivating garden peas. He found that his pea plants 

 differed from each other in very many characters. Tallness, col- 

 oration of seeds petals, and pods, and the hairiness, roughness, 

 or smoothness of skin on the seeds and stems were some of the 

 differences that he observed. Then he asked, " How does a partic- 

 ular quality carry over generation after generation ? " He pro- 

 ceeded to seek the answer to his problem by experimentation. 

 He selected tall plants and kept them in a certain garden plot. 

 Away from these he raised a plot of plants that were always short. 

 He called each group a pure-type. The unit character of height 

 was one particular trait in which he was interested. He crossed 

 pairs of plants which differed in this single character. He repeated 

 his experiments to investigate other out-standing characters. Tall 

 plants were crossed with short; plants with yellow seed coats 

 with those of green seed coats ; plants having smooth seeds with 

 those having rough seeds; hairy stemmed plants with hairless 

 stemmed ones. In each of these crosses he watched the behavior 

 of the variations of a single character only. After many experi- 

 ments, Mendel learned and made known some very important 

 principles. 



The Mendelian laws of inheritance. The Law of Dominance. 

 When two of the pea plants that differed from each other in one 

 characteristic were crossed, all the offspring resembled one of the 

 two parents in regard to that characteristic. If one parent were tall 

 and the other short, all of the next generation would be tall. 



