194 DISCOVERY CH. 



tall. This character of tallness was called by Mendel 

 " dominant," while the character of shortness, which 

 does not appear in the first generation of the hybrid 

 plants, was described as " recessive." 



The tall hybrids were then allowed to fertilise them- 

 selves, and it might be supposed that they would breed 

 true ; but that was not the case. After self-fertilisation 

 each hybrid produced offspring in which the two original 

 parental characters dominant and recessive were 

 exhibited in the ratio, on the average, of three to one, 

 -there being in the case of tall and dwarf peas three tall 

 plants to one short. From the dwarf plants, when 

 self-fertilised, or fertilised from the original short stock, 

 only dwarfs can be obtained henceforth ; in other words 

 the recessive minority of the second generation breeds 

 true. Of the three tall plants belonging to the same 

 generation, one possesses the dominant character alone 

 and will produce only pure-bred or tall plants, when 

 self-fertilised ; but the two remaining plants are cross- 

 breds and these on self-fertilisation again give the 

 mixed generation of three plants possessing the dominant 

 character of tallness to one plant having the recessive 

 character of shortness. 



The same simple rule was found by Mendel to be true 

 when plants differing in several characters instead of 

 one were cultivated ; and thousands of experiments 

 made by biologists since 1900 have shown that the 

 results of hybridisation discovered by him hold good 

 for specific characters exhibited by plants and animals of 

 many kinds. The work carried on by Mendel in the 

 seclusion of the cloister at Briinn has, indeed, put the 

 whole subject of heredity upon an entirely new footing, 

 and indicated a mode by which the isolation and per- 

 petuation of definite characters can be assured. 



