54 HEREDITY [ch. v 



Mendel's most important experiments were made 

 with races of the edible pea, which he grew in the 

 garden of his monastery. He found in peas several 

 characters which vary and are inherited discon- 

 tinuously, and he crossed together races which 

 differed in one or more of such characters, but in the 

 oflfspring and later generations he considered the 

 distribution of each character by itself, quite apart 

 from the other characters of the plant. As an 

 example we may take the character height or 

 tallness. Certain varieties of peas grow stems some 

 six feet in height, others are short and do not exceed 

 about two feet. The heights fluctuate about a mode, 

 but the smallest individuals of one race (grown under 

 proper conditions) are taller than the largest of the 

 other, and each race breeds true. Similar tall and 

 short races exist in the sweet-pea (fig. 7), the short 

 race being called 'Cupid' sweet-peas. When the 

 two races are crossed — and reciprocal crosses give 

 identical results — the offspring are not intermediate 

 but all are tall, perhaps taller than the tall parents. 

 When now these hybrid tails are self-fertilised, 

 among the plants produced some are tall and others 

 short, but again none are intermediate. Mendel 

 regarded the tallness or shortness as distinct alter- 

 native characters, and since tallness alone appears in 

 the fii'st cross, he spoke of it as ' dominant,' and the 

 shortness, which disappeared when crossed with the 



