158 BLASTOGENIC VARIATIONS. 



f erent ovules of the hybrids, and d and r those in pol- 

 len grains, then on crossing these hybrids haphazard, 

 the germ cells giving rise to the next generation will 

 unite so as to form Dd + Dr + dR -\-Rr. Now Men- 

 del found that it was perfectly immaterial whether the 

 dominant character belonged to the male or the female 

 plant, and so it follows that we should get twice as 

 many similar hybrid forms (Dr and dR) as of pure 

 dominant or pure recessive. 



If parental forms possessing two or more differentiat- 

 ing characters be crossed, the law of alternative herit- 

 age continues to hold, though it necessarily becomes 

 somewhat more complicated. For instance, Mendel 

 crossed seed parents with round seeds (A), and yellow 

 cotyledons (.?), with pollen from plants having angular 

 seeds (a), and green cotyledons (6). The hybrids 

 would therefore consist of plants with germ cells hav- 

 ing the characters AB, Ab, Ba, and db. These hybrids, 

 on crossing haphazard, would yield the following: 



(AB + Ab + Ba + o&) 2 = A*B* + AW +2A*Bb + 2AB*a + 



38 35 65 60 



4 ABdb +2 Aab* + 2 Ba?b + BW + S 6 9 

 138 67 68 28 30 



The figures underneath indicate the actual numbers 

 of plants obtained by Mendel from the 556 seeds 

 yielded by the 15 original hybrid plants. The average 

 numbers with two, three, and four characters are re- 

 spectively 34, 65, and 138, or very nearly in the theo- 

 retical proportion of 1 :2 :4. 



Mendel even took the immense trouble to cross 

 parents differing in respect of three characters, and he 

 found that the offspring of the resulting hybrids with 



