Lutz, Triploid Mutants in Oenothera. 4'2 1 



by the phenomena which he observed in the germ cells of the 21- 

 chromosome parental form. 



A number of theories have been offered to explain the origin 

 of the tetraploid condition in 0. yigas. One of these, namely that 

 of de Vries and Stomps, presupposing the union of two germ 

 cells each having the diploid number of chromosomes (and thereby 

 allowing for the possibility of a more frequent union of a haploid 

 and a diploid germ cell) is quite sufficient to explain the presence 

 of the 21-chromosome mutant in cultures of 0. Lamarckiana X O. 

 Lamarckiana, and the 22- chromosome mutant in the culture of 

 0. lata self-pollinated, as reported. 



Since a triploid condition is represented in the 21-chromosome 

 offspring of 0. Lamarckiana X ^- Lamarckiana and that which 

 may be termed triploid in the 21- and 22-chromosome offspring of 

 0. lata self-pollinated, the explanation which first suggests itself is 

 that of the union of a reduced and an unreduced germ cell. 



The question which next arises is whether this unreduced germ 

 cell was contributed by the male or female parent. 



We have the case of polyspermy in animals in which the 

 reduced female germ cell receives a double number of chromosomes 

 from the male, and the case of Ascaris in which a reduced number 

 of male chromosomes unites with a double number from the female. 

 From what w r e know of apogamy in plants, however, it seems 

 probable that reduction fails to take place in the female germ cells 

 more commonly than in the male. This assumption appears to be 

 supported by the presence of 2 lata -like hybrids in the culture of 

 0. lata X O.gigas and of 9 hybrids in a total of 61 for 1907 (3) and 

 1908 (58) having each a chromosome number of 28 (?), 29 or 30. 

 The simplest explanation for the origin of these 11 plants is that 

 of the apogamous development of unreduced female germ cells in 

 the two former cases, and the fertilization of unreduced female by 

 reduced male germ cells in the 9 remaining cases. 



A total of 80 offspring of 0. lata X 0. gtgas was grown in 

 1907(3) and 1908(77). Of this number fixations were prepared for 

 chromosome studies from 63; chromosome numbers were studied 

 in 61 and exactly determined in 52.- These 52 oft'spring were 

 distributed as follow r s: 



Number of chromosomes 15 21 22 23 29 31 ) 30 

 Number of individuals 2 16 25 3 2 4. 



31) One of the three plants of the 1907 culture was first reported (18) as 

 having 28 or 29 chromosomes. The number has since been exactly determined and 

 was found to be 29. Several metaphase figures of 28 chromosomes each were 

 counted iu one of the two plants marked 28 (?), but since only a few were 

 observed, and these did not demonstrate the number as clearly as I wished, I prefer 

 to label this plant (3368) as questionable. 



