HEREDITY AND EVOLUTION 251 
The improvement of cultivated plants has frequently been due 
to the selection of mutations. Red sunflowers and giant varie- 
ties of tobacco are examples of mutations. 
A character which results from a mutation may be considered 
as due to the modification of something already present rather 
than as the result of the addition of an entirely new factor. A 
mutam aay vary greatly or only slightly from the parent. 
The red sunflower affords a good example of a mutant. In the 
sunflower the so-called flower is, in reality, a head composed of 
many flowers packed close together. The central, or disk, flowers 
are small, while the outer, or ray, flowers are large and have 
a brilliant orange color. It is these ray flowers which are largely 
responsible for the attractive appearance of the head. In the year 
1910 a sunflower with chestnut-red rays was found by a road- 
side in Boulder, Colorado. The plant was very striking, and its 
presence could only be explained as due to mutation. In order 
to reproduce the plant it was necessary to cross it with a plant 
having ordinary orange-colored rays, as sunflower plants are not 
fertile unless cross-pollinated. In the F, generation of this cross 
about half the plants were red and the other half orange. Sub- 
sequently the red color proved to be a Mendelian dominant. 
Therefore the explanation of the fact that in the /, generation 
of the original cross half the offspring showed the red color and 
half the orange color would seem to be that the original red 
mutant was heterozygous and contained only one factor for red. 
An examination of the red color of the red sunflowers showed 
that the chestnut-red color was due to the fact that both a red 
pigment and the original orange pigment were present in the rays. 
By subsequent breeding, plants were obtained that had rays with 
the red and without the orange color. These flowers were wine red 
or old rose. The breeding was carried out in the following manner: 
Since the year 1889 there has been in cultivation a variety 
of sunflower called primrose, which arose as a mutant from the 
ordinary orange variety and which is pale yellow. This variety 
was crossed with the chestnut red. In the /, generation the 
offspring were all chestnut red, as the orange color dominates 
