850 
Journal of A^gricultural Research 
Vol. XXIV, No. 10 
The y factor in Gradus is linked with the a factor for white flowers; its 
allelomorph Y is linked with the A factor for colored flowers in Mummy. 
The proof of the presence of two factors for stipule shape in Gradus and 
Gradus rogue lies in the fact that no linkage exists between the X factor 
(the mutated form of the x factor of Gradus) in Gradus rogue and the a 
factor for white flowers as determined from an analysis of the F2 genera¬ 
tion of the cross Gradus rogue with Mummy. 
The allelomorph, in Mummy, of factor x is probably not identical with 
X but is very similar in its somatic expression. At least in combination 
with y of Gradus (the x'x'}^ segregates from the F2 generation of Rogue 
X Mummy), the x'x'3ry plants have stipules very nearly like Gradus 
type. The factor allelomorphic to x and found in Mummy is called 
x' to distinguish it from the x factor of Gradus. Additional evidence of 
a difference betvveen x and x' is the fact that x' has never been known 
to mutate to X when x' is present in the homozygous state. The factor 
x' is apparently more stable than x. 
In addition to the assumed inherent stability of the x' factor found in 
Mummy it is probable that the Y factor also acts as a stabilizer of the 
germ plasm. The heterozygous F^ plants of Gradus rogue X Mummy 
(YyXx') have a germ plasm which is certainly less affected by the 
presence of the X factor than is the heterozygous 'Kyeyy germ-plasm of 
Gradus rogue. With the Xx' combination, recurring somatic mass 
mutation to the extent obtaining in the Fj generation of Gradus type X 
Gradus rogue, does not occur. The various factors that entered the 
zygote take part in gamete formation at maturity and give rise to the 
expected F2 combinations. Although Y behaves as a stabilizer of the 
Fj germ plasm and retards mass mutation of x' to X, the extent of the 
influence is difficult to determine. Nor is it known to what extent, if 
any, senility affects the relation of the X and x' factors. It is possible 
that, with increasing age, the F^ plants exhibit a change in the muta¬ 
bility of x' to X, resulting in an increase of rogues among the F2 segre¬ 
gates. Since other disturbing causes than somatic mutation in the F^ 
hybrid may combine to upset the expected number or ratio of F2 recom¬ 
binations, the deviations of the observed number from the calculated 
number of variates in any one class can not be used, for the F2 data at 
hand, to approximate the rate of change of x' to X. 
That changes in the X factor may occur in the F^ hybrids here dis¬ 
cussed is indicated by the exceptional F^ plant (no. 9.727-6), which was 
similar in appearance and genetic behavior to the F^ hybrids of Gradus 
type X Mummy. Additional evidence of mutation of X to some* other 
form is shown in the behavior of two roguelike F^ plants (No. 9.722-1 
and No. 9.722-5). These plants apparently produced very few, or no, 
rogues in the next generation (families 0.1059 and 0.1093). The primary 
mutation or mutations of X in the F^ parents was here delayed until 
late in development and, while not affecting the soma, radically changed 
the genetic character of the microspores and macrospores. 
An analysis of the F3 generation of the cross Gradus rogue with Mummy 
substantiates the hypothesis of Mendelian inheritance of the rogue factors 
complicated by recurring somatic mutation. The number of segregating 
to nonsegregating F3 families is in close agreement with the theoretical 
number of i XX : 2 Xx' F2 rogue segregates expected from a mono¬ 
hybrid Fi generation. The ratio of XX to Xx' plants in the progenies of 
heterozygous F2 rogues is disturbed by the phenomenon of recurring 
somatic mutation. 
