From each of these experiments there could then result only the
following forms:--
1. _AB_, _ABb_, _AaB_, _AaBb_.
2. _AaBb_, _Aab_, _aBb_, _ab_.
3. _AB_, _ABb_, _AaB_, _AaBb_.
4. _AaBb_, _Aab_, _aBb_, _ab_.
If, furthermore, the several forms of the egg and pollen cells of the
hybrids were produced on an average in equal numbers, then in each
experiment the said four combinations should stand in the same ratio
to each other. A perfect agreement in the numerical relations was,
however, not to be expected, since in each fertilisation, even in
normal cases, some egg cells remain undeveloped or subsequently die,
and many even of the well-formed seeds fail to germinate when sown. The
above assumption is also limited in so far that, while it demands the
formation of an equal number of the various sorts of egg and pollen
cells, it does not require that this should apply to each separate
hybrid with mathematical exactness.
The first and second experiments had primarily the object of proving
the composition of the hybrid egg cells, while the third and fourth
experiments were to decide that of the pollen cells[40]. As is shown by
the above demonstration the first and second experiments and the third
and fourth experiments should produce precisely the same combinations,
and even in the second year the result should be partially visible in
the form and colour of the artificially fertilised seed. In the first
and third experiments the dominant characters of form and colour, _A_
and _B_, appear in each union, and are also partly constant and partly
in hybrid union with the recessive characters _a_ and _b_, for which
reason they must impress their peculiarity upon the whole of the seeds.
All seeds should therefore appear round and yellow, if the theory be
justified. In the second and fourth experiments, on the other hand,
one union is hybrid in form and in colour, and consequently the seeds
are round and yellow; another is hybrid in form, but constant in the
recessive character of colour, whence the seeds are round and green;
the third is constant in the recessive character of form but hybrid in
colour, consequently the seeds are angular and yellow; the fourth is
constant in both recessive characters, so that the seeds are angular
and green. In both these experiments there were consequently four sorts
of seed to be expected--viz. round and yellow, round and green, angular
and yellow, angular and green.
[40] [To prove, namely, that both were similarly differentiated, and
not one or other only.]
The crop fulfilled these expectations perfectly. There were obtained in
the
1st Experiment, 98 exclusively round yellow seeds;
3rd " 94 " " " "
In the 2nd Experiment, 31 round and yellow, 26 round and green, 27
angular and yellow, 26 angular and green seeds.
In the 4th Experiment, 24 round and yellow, 25 round and green, 22
angular and yellow, 27 angular and green seeds.
A favourable result could now scarcely be doubted; the next generation
must afford the final proof. From the seed sown there resulted for the
first experiment 90 plants, and for the third 87 plants which fruited:
these yielded for the--
1st Exp. 3rd Exp.
20 25 round yellow seeds _AB_
23 19 round yellow and green seeds _ABb_
25 22 round and angular yellow seeds _AaB_
22 21 round and angular green and yellow seeds _AaBb_
In the second and fourth experiments the round and yellow seeds yielded
plants with round and angular yellow and green seeds, _AaBb_.
From the round green seeds plants resulted with round and angular green
seeds, _Aab_.
The angular yellow seeds gave plants with angular yellow and green
seeds, _aBb_.
From the angular green seeds plants were raised which yielded again
only angular and green seeds, _ab_.
Although in these two experiments likewise some seeds did not
germinate, the figures arrived at already in the previous year were not
affected thereby, since each kind of seed gave plants which, as regards
their seed, were like each other and different from the others. There
resulted therefore from the
2nd Exp. 4th Exp.
31 24 plants of the form _AaBb_
26 25 " " _Aab_
27 22 " " _aBb_
26 27 " " _ab_
In all the experiments, therefore, there appeared all the forms which
the proposed theory demands, and also in nearly equal numbers.
In a further experiment the characters of floral colour and length of
stem were experimented upon, and selection so made that in the third
year of the experiment each character ought to appear in half of all
the plants if the above theory were correct. _A_, _B_, _a_, _b_ serve
again as indicating the various characters.
_A_, violet-red flowers. _a_, white flowers.
_B_, axis long. _b_, axis short.
The form _Ab_ was fertilised with _ab_, which produced the hybrid
_Aab_. Furthermore, _aB_ was also fertilised with _ab_, whence the
hybrid _aBb_. In the second year, for further fertilisation, the hybrid
_Aab_ was used as seed parent, and hybrid _aBb_ as pollen parent.
Seed parent, _Aab_. Pollen parent, _aBb_.
Possible egg cells, _Abab_. Pollen cells, _aBab_.
From the fertilisation between the possible egg and pollen cells four
combinations should result, viz.:--
_AaBb_ + _aBb_ + _Aab_ + _ab_.
From this it is perceived that, according to the above theory, in the
third year of the experiment out of all the plants
Half should have violet-red flowers (_Aa_), Classes 1, 3
" " " white flowers (_a_) " 2, 4
" " " a long axis (_Bb_) " 1, 2
" " " a short axis (_b_) " 3, 4
From 45 fertilisations of the second year 187 seeds resulted, of which
only 166 reached the flowering stage in the third year. Among these the
separate classes appeared in the numbers following:--
Class. Colour of flower. Stem.
1 violet-red long 47 times
2 white long 40 "
3 violet-red short 38 "
4 white short 41 "