BEHAVIOR OF PEDIGREE HYBRIDS 23 1 



mitted this character. Color residing in outer endosperm cell- 

 layers is similarly transmitted. 



Behavior of Pedigree Hybrids. — Let us now leave this 

 line of our discussion for the present and turn to the behavior 

 of pedigree hybrids, for in them we have the strongest evidence 

 that paternal and maternal chromosomes become segregated 

 in microspores and megaspores. 



It was Gregor Mendel, teacher of natural sciences in the 

 Realschule in Briinn, Austria, between 1853 and 1868, who, 

 as a result of a long series of experiments in hybridization, in- 

 spired by Darwin's then recently published Origin of Species, 

 discovered certain laws in the behavior of his hybrids, which 

 have recently risen to fame under the name of Mendel's Laws. 

 We will now relate some examples to illustrate the nature of his 

 results. 



Mendel crossed a variety of pea having lateral flowers with 

 one bearing terminal flowers, and found that the hybrid progeny 

 bore lateral flowers only (Fig. 132, A, B, C, D. Here Fj, Fj, F3 

 signifies ist, 2d, 3d filial generation), no matter which variety 

 was used as the mother or the father, and he therefore concluded 

 that, since both characters were in the blood of the hybrid, the 

 lateral character was dominant and the terminal character 

 was recessive. When these hybrids began to blossom all pos- 

 sibility of cross-pollination was excluded, and each was caused 

 to fertilize itself; and on planting the resulting seeds it was found 

 that each plant's offspring were lateral-flowered and terminal- 

 flowered in the ratio of three bearing lateral (Fig. 132, a, b, c 

 under F2) to one bearing terminal flowers {d). Self-fertilization 

 was continued in this generation, and the seeds of each plant were 

 planted separately, with the result that the terminal flowering 

 plants gave only terminal flowering offspring (Fig. 132, 4)^ — one- 

 third of the lateral flowering plants gave only lateral flowering 

 offspring (Fig. 132, i), while the remaining two-thirds gave both 

 lateral and terminal flowering individuals in the ratio of three 

 lateral to one terminal (Fig. 132, 2 and 3). 



In thus carrying on pedigree cultures where the seeds of each 



