FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 83 
Certain somatic characters of many mutant offspring of 0. La- 
marckiana X 0. Lamarckiana and of 0. Lamarckiana, selfed, indicate 
that a very large percentage of the mutant offspring of O. Lamarckiana 
have IS chromosomes and that a larger number of ly than of 14-chromo- 
some mutant offspring are produced hy this form. Not only does there 
appear to be a larger number of distinct types of 75- than of 14-chromosome 
mutants^ hut a higher percentage of 15- than of 14-chromosome mutant 
individuals produced by O. Lamarckiana. Many of the mutant off- 
spring of 0. Lamarckiana never have been brought to flower; further- 
more, new forms are appearing each year. It will be necessary to 
determine the somatic chromosome numbers of a large percentage of 
the mutant types produced by G. Lamarckiana ^ to bring the 15-chro- 
mosome forms to flower, to self flowers on all parts of the plants, to 
adopt methods which will secure the germination of all viable seeds, 
and to grow large numbers of offspring, — in order to ascertain whether 
15-chromosome forms are more commonly inconstant than constant. 
The majority of the 15-chromosome forms whose constancy we have 
considered have produced very few offspring, yet we may safely assert 
that the evidence available at present indicates that most 14-chro- 
mosome forms are constant and most i^-chromosome forms inconstant. 
Furthermore, although our present knowledge of the behavior of 
i4+-chromosome forms is very limited, largely owing to the infre- 
quency with which good pollen is produced by such forms, it may be 
stated that the evidence available at present indicates that inconstancy 
is commonly associated with the 14 -{--chromosome condition. It seems, 
however, that forms having twice 14 chromosomes are more likely to 
be constant — in the same sense that 0. gigas de Vries is constant — 
than those having more than 14, but fewer than 28, chromosomes. 
4. Factors Determining the Constancy or Inconstancy of 15-Chromosome 
Forms. 
De Vries obtained the same results from 0. scintillans selfed, as 
from 0. scintillans X O. Lamarckiana (pp. 257-262) ; also the same re- 
sults from selfed hybrid lata, descended through 0. lata X 0. La- 
marckiana from 0. lata X 0. semilata, as from 0. lata X 0. Lamarckiana 
('09, Vol. L, pp. 240, 360; '13, pp. 244-257). This led him to conclude 
that female gametes of 0. scintillans and this hybrid lata do not bear 
the same hereditary characters as the male gametes of these forms; 
that the characters of the mutant, in the first case, and of the hybrid 
