540 HEREDITY 



havior of the hybrid offspring in successive generations. His 

 plan was to cross plants differing in one or a few outstanding 

 characters, such as the color of flowers, height of plant, color and 

 shape of seeds, etc., and determine the laws governing the appear- 

 ance of these characters in the hybrid offspring. 



Material Chosen, — Mendel used great care in the selection 

 of the plants to be used in the experiment, for he realized that 

 the success of any experiment depends upon the choice of the 

 most suitable material. After careful consideration he chose 

 the Edible or Garden Pea as the chief plant with which to work. 

 The Garden Pea proved to be the most suitable plant because: 

 (1) it matures in a short time; (2) varieties in cultivation are 

 distinguished by striking characters recognizable without trouble; 

 (3) the plants are self-fertilized, and hence plants chosen for 

 parents would be pure, that is, they would have no hybrid 

 blood in them, and the hybrids and their offspring would not be 

 disturbed by crossing in the successive generations. 



Mendel's Experiments. — Mendel investigated pairs of char- 

 acters separately and in relation to each other, and extended his 

 investigations to include many pairs of characters, in order to see 

 if all appeared in the successive generations of offspring accord- 

 ing to the same law. His method of procedure may be shown 

 by describing his experiments with tall and dwarf Peas. A tall 

 Pea, having a height of 6-7 feet was crossed with a dwarf Pea, 

 having a height | to 1| feet. By means of forceps or other in- 

 struments and before the flowers were open, the anthers were re- 

 moved from the flowers of the plant selected as the mother plant, 

 and pollen from the pollen parent was applied to the stigma. 

 The hybrid seeds developed by the mother plant as a result of the 

 crossing were carefully collected. These cross-bred seeds were 

 planted and produced the first hybrid generation of plants, known 

 as the Fi generation in our modern terminology. The height of 

 each individual of this generation was carefully noted, and each 

 individual was compared with the parents in respect to tallness 

 or dwarfness. The individuals of this generation were allowed 

 to self-fertilize, and the seeds of each individual were collected 

 and planted separately. From these seeds he grew the second 

 generation or F^ generation according to modern terminology. 

 The individuals of the progeny of each of the Fi plants were 

 carefully compared with their parents and grandparents in re- 



