252 A TEXTBOOK OF GENERAL BOTANY 
the pale yellow and the red dominates the absence of red. In the 
fF’, generation there were four kinds of plants obtained: chestnut 
Chestnut rec 

Fig. 238. Diagram of inheritance of flower color 
in sunflower 
f represents a factor for the dominant character red ; 
r, the absence of this factor; O, the factor for the dom- 
inant color orange ; and 0, the factor for the recessive 
pale yellow. R and O together produce chestnut red 
red, orange, wine 
red, and light yel- 
low, approximately 
in the proportion of 
nine, three, three, 
one. ‘This is the 
dihybrid ratio and 
shows that in this 
case we are consid- 
ering two pairs of 
independent unit 
characters. The 
first pair is the 
dominant red, R, 
and the recessive, 
which is the ab- 
sence of red, 7; the 
second pair is the 
dominant orange, 
O, and the reces- 
sive pale yellow, o. 
By means of these 
symbols there is 
shown, in Fig. 238, 
the crossing of the 
chestnut red and 
the light yellow 
and the composi- 
tion of the 7, and 
F, generations. In 
the case of the red 
sunflower we see 
how a new variety can arise as a mutation, and how still other 
new varieties can be obtained by further breeding. 
