HETEROPLOIDS 



181 



The spontaneous occurrence of primaries and second- 

 aries is given in the next table. The primaries arise in 

 this way more frequently than the secondaries. Breed- 

 ing experiments have shown that whereas primaries may 

 occasionally throw secondaries, the secondaries regularly 

 throw their primaries more frequently than they throw 

 new mutants belonging to the other groups. Thus of 

 31,000 offspring from poinsettias about 28 per cent were 

 poinsettia and about 0.25 per cent were the secondary 

 wiry. Conversely, when wirys were the parents about 

 0.75 per cent of the offspring were the primary poin- 

 settia. 



Spontaneous Occurrence of Primary and Secondary (2n-)-l) Mutants 

 (Primaries are printed in capitals, secondaries in lower-case type.) 



The breeding experiments of "Wedge — a Secondary of 

 the Cocklebur group — furnishes the following evidence 

 as to the relation of secondaries to primaries. "Both 

 Poinsettia and its Secondary Wiry give trisomic ratios 

 for the color factors P, p, but give disomic ratios for 



