206 MENDELISM 
3p, Iw). Since g is absent from all the members of 
the series enclosed in the bracket, these appear white, 
or nearly so, the total number of whites being thus 16. 
And the numbers obtained in an actual experiment 
accorded closely with the expected ratio 27: 9: 9: 3: 16. 
Among the sixteen whites, some will be bearing the 
factors for m and #, others that for # only, others that 
for m only, whilst one in sixteen will contain neither of 
these factors. Until such invisible differences between 
the different white plants are actually proved to be 
present the whole account so far given will remain more 
or less hypothetical. The proof is obtainable by cross- 
ing the different whites with a pure grey strain. The 
grey factor being thus introduced, the whites which 
contain a # or an m factor will exhibit the same in 
their offspring. A number of the whites obtained in 
F, and in Jater generations were actually crossed with 
the same grey-seeded plant. Some of the offspring 
showed both the maple and the purple character, 
others the maple without the purple, others the purple 
without the maple, and others, again, showed neither ; 
the seeds of these last being exactly like those of the 
grey parent owing to simple dominance of the grey 
allelomorph over white. 
The first example of this kind of phenomenon to 
be observed in the case of animals was one described 
by the French zoologist Cuénot. Cuénot’s original 
account has had to be somewhat modified in view 
of more recent work by Miss Durham, and the latest 
account of the facts runs as follows. For the sake 
of simplicity we shall deal in the first instance with 
