THE LAAV OF SEPARATION OF CHARACTEES IN CROSSES. 247 
From the main principle of the law of separation various other con- 
sequences may be deduced, which admit of experimental proof. 
For instance, if we fertilise a cross with the pollen of one of the two 
parents, or, vice versa, fertilise one of the parental types with the cross, 
we obtain : — 
(d -f r) d = d^ + dr, and 
(d + r) r = dr+ 
In the first case, therefore, some of the resulting plants are crosses, 
and the others are pure forms, but all display the dominant character. 
In the second case, some are hybrids with the dominant, and others 
are pure forms with the recessive character, and both in equal numbers ; 
thus we have — 
50 per cent, dominant (hybrids). 
50 per cent, recessive (pure). 
I found, for instance, — Year of 
Trial. 
Clarkia pulchella x x white 50 per cent. 1896 
(Enothera Lamarckiana x xbrevistylis 55 „ 1895 
Silene Armeria x x white 50 1895 
The same law applies, as I have said, even when we investigate 
I)i-hybrids, or study two pairs of antagonistic characters of Polyhybrids. 
I select, as example, a cross of mine in 1897, effected between the prickly 
Datura Tatula ^nd Datura Stramonium inermis. According to a known 
rule with crossed plants, it is in this case quite immaterial which type 
bears the pollen and which the egg-cells. The hybrids bear blue 
flowers and prickly fruits. Some flowers were fertilised with their own 
pollen and their seed sown in September 1899. Already at the germina- 
tion it was possible to tell by the colour of the stalks which were blue 
flowering and which were white. I found — 
Blue (dominant + hybrid) 72 per cent. 
White (recessive) 28 ,, 
which was confirmed by the flowers afterwards. 
As regards the fruits, there were — 
Thornless among the blue, 26*8 per cent. 
„ „ white, 28-0 „ 
Average 27*4 „ 
From this can be calculated for almost any case the composition of 
the offspring. If we, for instance, name A the one and B the other pair 
of antagonistic qualities, we shall have for Di-hybrids for 
A 25 % dom. 50%dxr 25 % rec. 
B 6-25 d, 12-5 dr, 6-25 r. 12-5 d, 25 dr, 12-5 r7 6-25 d, 12-^dr, 6*25 r^ 
There are, therefore, 6*25 per cent, of examples which are purely 
dominant in both respects, and precisely as many which are purely reces- 
sive in both respects, and so on. 
Utihsing the principle further, that the crosses display the dominant 
traits, we shall find the visible characters of the offspring to stand thus : 
1. Adom.-f Brec. . . 18*75 per cent. 
2. A rec. -f B dom. . . 18'75 
3. A dom. -F B dom. . . 56-25 „ 
4. A rec. -f B rec. . . 6-25 
