HEREDITY 229 



are yellow. The character g is thus separated from the 

 character y. 



(3) The green peas obtained as in (2) are now sown and raised 

 to plants and the latter are selfed. All the peas that they bear 

 are green ones. If these peas are again sown, and if the resulting 

 plants are selfed, all the peas that they bear will be green ones 

 and so ad i?ifinttum. Thus a Mendelian " Pure race " — *' pure " 

 in respect of the colour of the peas, is obtained. 



(4) The yellow peas obtained as in (2) are sown and raised 

 to plants and the latter are selfed. They will bear both yellow 

 and green peas : one-third of all the plants bearing yellow peas 

 and two-thirds bearing both green and yellow peas. The yellow- 

 peaed plants of the one-third fraction are a " pure race " (as in 

 (3)) in respect of yellowness, but the two-thirds fraction, when 

 sown and grown and selfed, will again bear both yellow and green 

 peas. 



From these simple experiments we can make certain provisional 

 conclusions : 



(a) In hybridizing Mendelian races of pea-plants the ensemble 

 of systematic, or specific characters, E appears unchanged in the 

 progeny. 



(b) In hybridizing Mendelian races of pea-plants we can obtain 

 progeny that display only one of the two characters of the races 

 but have the potentialities of displaying, in their progeny, the 

 other character (the *' Principle of Dominance and Recessiveness "). 



(c) In such progeny that display a dominant character but have 

 also a recessive, or potential one, further breeding can result 

 in progeny that display both characters (the " Principle of 

 Segregation "). 



{d) There are pairs of characters (green peas and yellow peas, 

 tallness and dwarf ness, round peas and wrinkled peas and so on). 

 If one of a pair of characters is displayed the other one is not 

 displayed. The pair of characters are called allelomorphs. (This 

 is the " Principle of Allelomorphism.") 



Proceeding in the same way we can hybridize pea-plants that 

 have 2, 3, etc., pairs of allelomorphic characters. Thus there 

 may be yellow peas that may be round or wrinkled and green peas 

 that may be round or wrinkled. There may be tall pea-plants 

 that bear green peas that may be round or WTinkled, dwarf pea- 

 plants that bear green peas that may be round or wrinkled and so 



