HYBRIDIZATION IN PEAS 197 



subsequent generations. The character which appears in the 

 hybrid is said to be dominant, while that which is suppressed is 

 said to be recessive. In the case of these peas, then, one character 

 is always dominant over the other in the hybrid, and, moreover, 

 it is always the same character, and it does not matter whether 

 it is derived from the male or from the female parent. Thus the 

 round form of seed is dominant over the wrinkled, the yellow 

 colour of the seed-contents over the green, and so on. 



Having obtained the hybrids, the next step was to follow the 

 history of the offspring throughout successive generations. For 

 this purpose the flowers of the plants raised from the hybrid 

 seeds were allowed to fertilize themselves with their own pollen, 

 no further crossing being permitted. The seeds thus obtained 

 (constituting the F 2 or " second filial " generation) were now 

 again apparently of two kinds, resembling the two original parent 

 forms from which the hybrid was produced. Moreover, these two 

 kinds occurred in definite proportions, three of the dominant to 

 one of the recessive three round seeds to one wrinkled, three 

 yellow to one green, and so on. Of course, these proportions are 

 only averages, and, in order to eliminate errors of chance, large 

 numbers of observations must be made the greater the number 

 the more reliable the result. To take an actual example from 

 Mendel's work, 7,324 seeds were obtained in the second trial year 

 from the hybrids between round and wrinkled. Of this number 

 5,474 were found to be round, and 1,850 wrinkled showing the 

 ratio of 2'96 to 1. Again, out of 8,023 seeds produced by the 

 hybrids between green and yellow, 6,022 were yellow and 2,001 

 green, the ratio being 3*01 to 1. These experiments have often 

 been repeated during recent years, especially by Mr. A. D. 

 Darbishire, 1 and it is found that the average ratio of three to one 

 is always maintained. 



The significance of this proportion is not at first sight obvious. 

 It is necessary to continue the experiment for at least another 

 generation in order to gain further insight into the matter. We 

 have as the result of the self-fertilization of our hybrids 

 apparently only two kinds of seeds or plants, which we may 

 call D, showing the dominant character, and R, showing the 

 recessive character, in the proportion of 3 D to 1 R. If these 



1 Some beautiful illustrations of Mendelian results in both plants and animals 

 are given in Mr. Darbishi re's recent work "Breeding and the Mendelian Discovery " 

 (Cassell & Co., Ld., 1911). 



