416 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
individuals of the F, generation which showed the blend. By 
inbreeding the pink hybrids Correns obtained the perfect 1:2:1 ratio, 
that is, 1 red like one grandparent, 2 pink like the hybrid parent, and 
1 white like the other grandparent. Segregation was evidently taking 
place, the only unusual thing being the appearance of the F, indi- 
viduals, and that was explained immediately as failure of dominance 
(see Fig. 78). 
The question this introduces, therefore, is that of a mechanism 
which could account for such a result. The easiest explanation 
offered is that the red parent was a homozygote for redness (double 
dose) and the hybrid a heterozygote (single dose); the inference is that 
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Fic. 78.—Diagram illustrating blending inheritance, discovered by Correns 
in Mirabilis Jalapa. (From Coulter and Coulter.) 
a single dose produces pink while a double dose produces red. A 
theoretical explanation of this occasional difference in the result of 
double and single doses is as follows. Imagine that the body cells 
of a plant have a certain capacity for expressing hereditary characters. 
In such a case, just as a given quantity of solvent can dissolve only a 
given amount of solute, so the body cells can express hereditary charac- 
ters only to a definite limited extent. In the four-o’clock a single dose 
of redness may be thought of as half saturating the body cells, while a 
double dose completely saturates them. In cases showing complete 
dominance, however, a single dose completely saturates the cells and a 
double dose can do nothing more. This analogy assists in visualizing 
on the one hand the necessary mechanism of blends (apparent failure 
