Lutz, Triploid Mutants in Oenothera. 4^5 



more light upon the subject it will be well to consider the possibility 

 of some other explanation for the origin of the 21 -chromosome 

 offspring of 0. lata self-pollinated, and 0. lata X 0. Lauiarcldana. 



We know that irregularities have been found in both the 

 heterotypic and homotypic divisions of the male germ cells of the 

 Oenotheras. 



We have seen that the chromosome numbers of certain offspring 

 of 0. lata X 0. yiyas indicate that these hybrids may have been 

 derived from unreduced female germ cells. Furthermore, Gates (14), 

 in testing for apogamy in 0. lata, obtained 3 seeds from the capsules 

 of guarded, unfertilized flowers, and Blaring hem has recently 

 reported (1) that Miss Thomas has discovered apogamy in 0. biennis. 



On the basis of these facts and indications. Professor V.Greg o ire 

 has suggested that a further irregularity of division may be found 

 to occur in the male and female germ cells of Oenotheras, and I 

 have his very kind permission to offer this suggestion here. 



Professor Gregoire's hypothesis presupposes that the majority 

 of somatic chromosome numbers in Oenothera are the result of 

 germ cell behavior as follows: 



1. Irregular distribution of chromosomes as observed in the 

 pollen mother-cells (and believed to occur also in the embryo sac 

 mother-cell) resulting from one (or possibly more occasionally) pas- 

 sing to the wrong pole of the spindle, thereby producing two sets 

 of daughter-nuclei, one having a number of chromosomes in excess 

 of that of the normally reduced number, another having a number 

 which is less than that of the normally reduced number. It is 

 assumed that the former are functional, but it is possible that the 

 latter may be so only when 7 or more chromosomes are present, 



- as would be the case with a 13-chromosome (). yiyas germ cell, 

 for example. 



2. The failure of one or more chromosomes to be included 

 within a daughter-nucleus, or the daughter nuclei at the heterotypic 

 or homotypic mitosis, or both. It is possible that functional germ 

 cells may result only when retaining 7 or more chromosomes. 



3. The production of functional female germ cells (and possibly 

 also male) with the unreduced number of chromosomes '- - resulting 

 from the arrest of the heterotypic mitosis before the division of 

 the nucleus has taken place. 



4. Degeneration of a portion of the chromosomes, in certain 

 forms, during the maturation process. 



These conditions alone are sufficient to explain the origin of 

 all the chromosome numbers in question. However, since many 

 may also be otherwise explained, a fifth possibility is offered for 

 consideration. 



