HERITABLE DIFFERENCES 59 



the mutation, (Enothera lata, which has 15 chromo- 

 somes instead of 14, the typical number for 0. 

 lamarckiana from which it sprang. What occurs in 

 the formation of this mutation is that for some reason 

 0. lamarckiana during reduction division instead of 

 dividing as usual into 7-7 makes the unequal division 

 of 6-8, a phenomenon known as non-dis junction 

 (Bridges). When this 8-chromosome gamete joins 

 with a normal 7-chromosome gamete the new mutant 

 number of 15, characteristic of O. lata, is the result. 



Gates and others in their extensive cytological 

 studies on (Enothera mutants, have found not only 15 

 chromosomes instead of 14 but also, associated with 

 various other mutations, the abnormal numbers of 16, 

 20, 22, 23, 24, 27, 28, 29, and 30. 



(Enothera gigas is a mutant in which 28 chromo- 

 somes, or twice the normal number, appear and, 

 moreover, these chromosomes represent actually twice 

 the original amount of chromatin material. "Gigas" 

 mutants have been found in various other forms, such 

 as the tomato (Winkler), the jimson weed or Datura 

 (Blakeslee and Belling), Primula (Gregory) and 

 Narcissus (Stomps), and they are always character- 

 ized by a doubling of the chromosomes. This condition 

 is termed tetraploidy because it shows four times the 

 gametic number of chromosomes. 



When a normal diploid Datura is crossed with a tet- 

 raploid gigas individual, a triploid mutant results 

 with a different constellation of somatic characters so 

 that the best of evidence is now at hand that one 

 category of mutations, at least, that of chromosomal 



