10 MENDELISM 



contrasted characters of the parents reappeared in one or 



other of the offspring of the hybrids. 



Pure-bred tall peas bred amongst themselves breed 



true, i. e. they produce only tall plants ; similarly, the 



dwarfs breed true amongst themselves ; but these hybrids, 



though apparently like the tall parent, do not breed true, 



but produce both tails and dwarfs. Now this is a most 



remarkable fact. In the first generation of hybrids the 



dwarf character has disappeared ; apparently it has been 



destroyed, and yet it reappears in the offspring of these 



hybrids. The two kinds, the dwarfs and tails produced by 



the hybrids, appeared, however, in unexpected proportions, 



for there were always three tails to one dwarf, i. e. three 



dominants to one recessive ; and this proportion of three 



dominants to one recessive holds good, not only for 



stature, but for whatever pair of contrasted characters be 



experimented with. This is represented by the following 



diagram — 



D x R 



D 



ill i 



D D D R 



It is useful to employ some concise terms to indicate 

 each of these three generations respectively. The first is 

 called the "parental generation," and is indicated shortly 

 by the letter P. The second is the " first filial generation," 

 and indicated by Fj (the word "filial " being derived from 

 the Latin word for son or daughter). The third generation 

 is called the " second filial generation," and is indicated by 

 Fij. If D represents a coloured flower, and R a white 

 one, then in the Fj generation we get only coloured flowers, 

 and in the Fij generation we get three plants bearing 

 coloured flowers to one bearing white flowers, and so on 

 with the other characters named. 



