126 REPORT OF THE CONFERENCE ON GENETICS. 
shanks was found to be incomplete but regular, while segregation was 
irregular, but gametic purity evident, the unit-characters being apparently 
presence and absence of shank feathers. 
The remaining pairs of Mendelian characters may be respectively 
regarded as presence and absence of crest, absence and presence of yellow 
pigment in the shanks, absence and presence of black pigment in the 
plumage, absence and presence of yellow pigment in the plumage. It 
will be noted that presence is dominant over absence in all cases except 
the black and yellow pigments, in which presence is apparently recessive 
though incompletely. 
HorsEs. 
In my investigations in coat-colour in thoroughbred horses, I have 
found that chestnut colour is a Mendelian character, recessive to both bay 
and brown, which are dominant characters. 
The unit-characters in this case are apparently presence and absence 
of black pigment in the points on a basis of red. 
SUMMARY OF EXPERIMENTS. 
From the brief survey given above, it will be seen that out of a total 
of 44 pairs of Mendelian characters met with in my experiments with 
plants and animals, no less than 41—or rather more than 93 per cent.— 
may be regarded as favourable to the hypothesis of presence and absence 
of unit-characters ; the remaining three—or rather less than 7 per cent.— 
being more favourable to Mendel’s original view of contrasting characters. 
Further experiments and the observations of others are necessary to 
determine the question, but in the meantime it may be interesting to 
inquire into the possible behaviour of the factors of these unit-characters 
in the processes of fertilisation and gameto-genesis. 
THE BEHAVIOUR OF UNIT-CHARACTERS IN FERTILISATION. 
In pure breeding, Mendel presumed that two like factors pair in the 
process of fertilisation—one factor from the male parent and one from 
the female parent—and when the resulting zygote produces gametes the 
two factors segregate, one factor going into one gamete and the other 
into another. In cross-breeding, Mendel presumed that two unlike but 
contrasting factors pair in fertilisation, and when the resulting hybrid 
zygote produces gametes, the two contrasting factors segregate, one going 
into one gamete and the other into another: e.g. a pea with green coty- 
ledons produces gametes carrying the factor G, and a pea with yellow 
cotyledons produces gametes carrying the factor Y. Then the green 
pea (G) self-fertilised, or fertilised with another green pea (G), produces 
a zygote (GG) which is green, and this produces gametes carrying G. 
Similarly a yellow pea self-fertilised produces a yellow zygote (YY), 
which produces gametes carrying Y. When a green pea is cross-fertilised 
by a yellow pea, the hybrid yellow zygote is YG, and this produces two’ 
kinds of gametes, Y and G. 
This is Mendel’s view of the process—presuming, as he did, that the 
unit-characters consist of pairs of contrasting characters, The hypothesis 
