Variation and Heredity 283 
forms which do not subsequently vary. The remainder are 
still mixed or hybrid in character. By successive self-fertili- 
zations it is possible gradually to separate out from these the 
pure types of which they are compounded. 
Without going into further detail it may be stated that the 
offspring of the parent hybrids, having two pairs of differen- 
tiating characters, are represented by the series : — 
AB Ab aB ab 2ABb 2aBb 2 Aab 2ABa 2 AaBo 
This series is really a combination of the two series :— 
A+2Aa+a 
B+2£B6+6 
Mendel even went farther, and used two parent varieties 
having three differentiating characters, as follows :— 
ABC seed parent abc pollen plant 
A form round a form angular 
{2 albumen yellow {i albumen green 
C seed-coat grey brown c seed-coat white 
The results, as may be imagined, were quite complex, but 
can be expressed by combining these series : — 
A+2Aa+a 
B+2B80+6 
C+2Cc +e 
In regard to the two latter experiments, in which two and 
three characters respectively were used, it is interesting to 
point out that the form of the hybrid more nearly approaches 
“to that one of the parental plants which possesses the great- 
est number of dominant characters.”’ If, for instance, the seed 
plant has short stem, terminal white flowers, and simply 
inflated pods; the pollen plant, on the other hand, a long 
stem, violet-red flowers distributed along the stem, and con- 
stricted pods,—then the hybrid resembles the seed parent 
only in the form of the pod; in its other characters it agrees 
