HEREDITY AND EVOLUTION 237 
describing the heights of the plants. Z represents tallness; D, 
dwarfness; and (D), dwarfness which is dominated by tallness. 
In the case just discussed, when tall plants were crossed with 
dwarf ones, their offspring were all tall. If plants with two 
opposite characters are crossed and their offspring show one of 
the characters and no influence of the other, then the character 
which appears in the offspring is said to dominate, or to be a 
TALL DWARF 
(ee rep se poesia sma 
ALL HYBk 
T YBRID F 


ALE NUCL, 
Fig. 233. Diagram showing inheritance of tall and dwarf characters in 
peas; also inheritance of factors for tallness 7’ and dwarfness D. (D) sig- 
nifies dwarfness dominated by tallness 
dominant character. A character which does not appear is said 
to recede, or to be a recessive character. In this case tallness is 
a dominant character as compared with dwartness. Dominance, 
like purity of gametes, is an important Mendelian principle. In 
the case of the four-o’clock plants the red color of the flowers 
is not nearly so dominant as is tallness in peas. The red color 
of the four-o’clock is said to be incompletely dominant. 
In different cases there may be various degrees of dominance. 
In some plants flower color may be just as dominant as tall- 
ness in peas, while in other plants length may be only partially 
