344 THE POPULAR SCIENCE MONTHLY 
nished the pollen and half from the plant to which it has been applied. 
If one studies the characters of several such hybrids, he finds many sur- 
prising facts. It usually makes no difference which plant is the mother 
plant, the result is the same. Certain characters are found in the hybrid 
that are identical with those possessed by the male parent and other 
characters the same as those possessed by the female parent. Other 
characters appear to have resulted from the blending of those of the 
two parents, while still others appear to be entirely new. The plant 
may be sterile if the cross is between widely differing species, but if it 
is fertile and the flower of the hybrid is self-fertilized, the plants re- 
sulting from this seed present still more surprises. For example, if 
one has crossed a pear-shaped yellow tomato with a round red tomato, in 
the second hybrid generation he will find individual plants bearing fruit 
of four kinds, pear-shaped yellow and round red, as were the two parents, 
and in addition pear-shaped red and round yellow. In other words 
all possible combinations occur and in definite proportions. Stated as 
a principle it may be said that where either of the parent plants pos- 
sesses characters absent from the other, the potential characters remain 
pure in the germ cells of the hybrid and recombine as if by chance. 
This is the most important feature of the only law of heredity of which 
there is any exact knowledge—the law of Mendel. Let us illustrate the 
action of the law. Such a character as starchiness, as shown in “ flint ” 
maize, is either present or it is not present. The flinty appearance of 
the seed is due to the possession of some character that causes the 
maturation of plump starch grains. When this character is absent, the 
seeds dry up without maturing their starch grains, and present 
the wrinkled appearance common to sweet maize. Pairs of char- 
acters such as these, affecting a certain plant structure, are called con- 
trasted or allelomorphic pairs. When a sweet maize is crossed with a 
flint maize, the resulting seeds are all flint like. That is, the dominant 
character or the character that calls for the presence of the structure 
or compound in question, manifests itself in the first hybrid generation. 
Complete dominance, however, is not a general phenomenon in crosses 
and as its importance is slight as compared with the second law, that 
of segregation of the pure characters (potentially) in the germ cells 
of the hybrid, we will discuss it no further. The second law predicts 
that in the generations succeeding a cross, plants grown from the self- 
fertilized seeds of the hybrid reproduce both contrasted characters in 
the proportion of three of the dominant or “ presence ” characters to 
one of the recessive or absent character. Furthermore, inbred or self- 
fertilized plants bearing the recessive character continue ever after to 
breed true, while of those plants bearing the dominant character one 
third are pure and breed true while two thirds are hybrids and again 
throw the recessive character in one fourth of their offspring. 
