184 THE THEORY OF THE GENE 



lent V is the most common form of union (48) ; next in 

 frequency is the ring-and-rod type (33) ; then the Y (17) ; 

 the straight chain (9) ; the ring (1) ; the double ring (1) ; 

 the ring of two with the third member left over (9-f-). 



From ten of the primary 25-chromosome forms 



V 



O 8 6 I 



48 33 17 9 1 1 9+ 



From ei§ht of the secondary 25-chrom. forms 



O0o 



26 13 1 3 2 51 Z0+ 



Fig. 104. 



Methods of union of the three chromosomes of a trisomic type of 



Datura. (After Belling and Blakeslee.) 



Since chromosomes are supposed to conjugate by like 

 ends coming together it is reasonable to assume that, in 

 these types, like ends (a and a, Z and Z) are still in con- 

 tact (see Fig. 104, upper row). 



In the lower row of Fig. 104 the different ways in which 

 the three chromosomes of the secondary types are united 

 are shown. In general the types are the same as those of 



