Gates .— The Trisomic Mutations of Oenothera . 547 
chromosomes have reached one daughter nucleus, six the other, while the 
fifteenth is left out in the cytoplasm. As is usual, a number of these 
chromosomes already show the split for the homotypic mitosis. 
Discussion. 
It has long been recognized that if the chromosomes of Oenothera are 
differentiated from each other in their hereditary qualities, as they clearly 
are in some organisms, then seven different types with 15 chromosomes 
might be expected. For a number of years Oe. lata , or the lata- like 
assemblage of forms, was the only mutation in which the chromosome count 
of 15 was clearly authenticated. The possibility remained either that 
any chromosome might constitute the extra one and give rise to a lata- like 
condition, or that the disturbance of duplicating one of the other chromo¬ 
somes was so great that the result was non-viable. It seems highly prob¬ 
able that non-disjunction of any of the seven pairs of chromosomes may 
take place, but it was possible that only one of the seven simple trisomic 
types (to use Blakeslee’s term) was viable. This possibility was perhaps 
strengthened by the discovery (Blakeslee, Belling, and Farnham, 1920 ) that 
Datura , which has twelve pairs of chromosomes, produces twelve trisomic 
mutations (i. e. forms with an extra chromosome), most of which have, like 
Oe. lata , high pollen sterility and transmit their characters almost entirely 
through the female sex. For since in Datura only one chromosome in 
twelve is duplicated, the germinal disturbance will be less than in Oenothera , 
where a chromosome constitutes one-seventh of the whole chromosome 
series. 
In recent years, however, a long array of 15-chromosome mutants in 
Oenothera has been demonstrated. Indeed the number now far exceeds 
the seven types originally anticipated, and this raises a number of interest¬ 
ing questions regarding the relationship and manner of origin of these 
types. Blakeslee has also found two additional Datura mutants with 25 
chromosomes, which he interprets as due to the presence of another genetic 
factor in certain trisomic forms. It may be pointed out here that Black¬ 
burn and Harrison ( 1921 ), in their studies of chromosomes in the roses, 
have found one plant of Rosa pimpinellifolia with sterile anthers and 15 
instead of 14 chromosomes. But they apparently observed no other differ¬ 
ences between this plant and the type. We may now enumerate the 
various Oenothera forms in which 15 chromosomes have been found. They 
are summarized in the following table. A (?) indicates either that the 
number of chromosomes is inferred from the genetic behaviour, or that it has 
not been determined with certainty. 1 
1 It may be pointed out that Lehmann ( 1922 , pp. 366-99) has treated all these forms with an 
extra chromosome in a somewhat different way in his ‘ Oenotheraforschungen ’, and Tischler ( 1922 ? 
pp. 604 ff.) has also treated the subject from the cytological point of view. 
