72 F. Keeble , Miss C. Pellew and W. N. Jones. 
contains dominant white (W), yields an F x containing magentas as 
well as whites. Therefore plant E cannot be pure with regard to 
the dominant white factor (YVW) ; for, if it were, all the plants of 
the cross D x E would be white. It must consequently he of the 
constitution ww or Ww. If it is the former, it cannot, since it is 
white, contain the magenta colour factor M. Its complete consti¬ 
tution with regard to these factors must therefore be ww mm. So 
that D x E=Ww Mm x ww mm, and the gametes produced are 
of the constitution :— 
Gametes of plant D :— WM, Win, win, wM : 
Gametes of plant E :— 4 wm: 
giving zygotes, 
4 Ww Mm : 4 Ww mm : 4 ww mm : 4 ww Mm 
—- ^ 
12 white : 4 magenta, 
as compared with the actual numbers, 
Obtained, 36 white : 10 magenta. 
Calculated, 34-5 white : 11-5 magenta. 
On the other hand, if plant E contain dominant white (W), its 
possible complete constitutions are : - Ww MM, Ww Mm, Ww mm. 
The first two possibilities, however, are negatived by the fact 
that E selfed gives an Fj all white. In the case of the third 
D x E=Ww Mm x Ww mm, which would produce zygotes in 
the ratio :— 
6 WM : 6 Wm : 2 wm : 2 wM 
N --' 
14 white : 2 magenta. 
Since, however, the experimental numbers are 36 white, 10 
magenta, the most probable constitution for plant E is ww mm, 
i.e., it is recessive to both negative magenta and dominant white. 
Cross F x F. Though the number (5) of plants in the F, ol 
plant F selfed is too small to throw certain light on the gametic 
constitution of plant F, we record our attempt to determine this 
constitution. 
Since the F t of the cross F x E contains magenta-flowered 
plants and since plant E is recessive to both magenta colour factor 
and dominant white factor, i.e., is ww mm, plant F must contain 
the magenta colour factor (M). And, since plant F is itself white, 
if it is carrying magenta it must also he carrying the dominant white 
factor (W). It cannot, however, be carrying pure W, for, if it were, 
the cross F x E would yield an F x of all white-flowered plants. 
Therefore the gametic constitution of plant F is Ww MM or Ww Mm. 
