THE LAW OF SEPARATION OF CHARACTERS IN CROSSES. 245 
If this rule be appHed by way of analogy to other cases, we shall 
occasionally find it to conflict with the accepted systematic arrange- 
ment, e.g. — 
Dominant Recessive 
Datura Tatula D. Stramonium 
Zea Mays (naked- seeded) Z. cryptosperma 
With specific crosses (Polyhybrids), where the mutual ages of the 
parents are usually unknown, it may be possible to arrive at some con- 
elusions in this direction through experimental crosses ; with respect to 
the colour of the flowers for instance : — 
Dominant Recessive 
Lychnis diurna (red) L. vespertina (white) 
The Latv of Separation of Characters in Crosses. 
In the cross the two antagonistic characters exist as associated but 
separate parts. In the vegetative development, as a rule, only the 
dominant one becomes visible. Exceptions are rare ; many partial 
separations aftbrd an example. Thus Veronica longifolia (blue) x F. 
longifolia alba often produces, in my garden, spikes bearing flowers blue on 
one side and white on the other. 
At the formation of the pollen grains and egg-cells the characters 
separate. The single pairs of antagonistic characters thereupon act 
independently of each other. From this separation results the law that — 
The pollen grains and ovules of Monohybrids are not crosses, but 
belong entirely to the one or the other of the two parental types. 
For Di-Polyhybrids the same law obtains with respect to each 
character regarded by itself.* 
By this principle it is possible to calculate the composition of the 
progeny, and by means of this calculation the validity of the law can be 
experimentally determined. In the simplest case the separation 
obviously takes place in equal halves, and we therefore get — 
50 per cent. dom. + 50 per cent. rec. pollen grains 
50 per cent. dom. + 50 per cent. rec. egg-cells. 
If we take d = dominant and r = recessive, fertilisation yields : 
(d-f r) (d + r)=d2 + 2 dr + r^ 
or 25 per cent, d + 50 per cent, dr-t-25 per cent. r. 
The individuals d and d^ have only the dominant, and the examples 
r and r^ only the recessive character, while the dr obviously are crosses. 
With self-fertilisation, whether isolated or in groups, the crosses of 
the first generation consequently yield as regards each single character — 
25 per cent, examples with the paternal character. 
25 ,, „ „ maternal ,, 
50 „ ,, which again are crosses. 
According to the first principle the crosses have the dominant 
character, and we get therefore 
75 per cent, examples with the dominant character. 
25 „ „ recessive „ 
* The combinations occur in accordance with the calculus of Chance. 
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