186 



THE THEORY OF THE GENE 



at which like genes come together. The result will give 

 two chromosomes each having its two ends alike, i.e., one 

 has A and A at its ends, the other Z and Z. If now such a 

 chromosome becomes in the next generation a member 



Primary 2n+l plants 



Secondary 2n + l plants 



A A 



Z 



Fig. 106. 



Diagram illustrating possible types of conjugation of three chro- 

 mosomes of trisomic types. (After Belling and Blakeslee.) 



of a trivalent group, it is possible to construct such modes 

 of union as indicated in Fig. 106, where in a Z-Z chromo- 

 some, combined with two normal partners, like ends meet 

 each other. 



If these rings, peculiar to the secondaries, can be ac- 

 counted for in the way suggested, it follows that one of 



