MUTATIONS 271 
following the discovery of the mutant stalk it was carefully lifted and 
the corm from which it grew was separated from the cluster of white- 
flowering corms. It was observed that there were smaller corms located 
very close to the mutant corm. The following spring one flower stalk 
bore red and white and the other only red flowers. In gladiolus the 
young corms push out from near the base of the old one. Hence the 
original mutant corm must have consisted partly of cells capable of 
producing red pigment in the flowers. That the cells having this altered 
chemical constitution comprised about one-half of the corm is indicated 
by the position of the red and white flowers on the stalk. This illustra- 
tion is hardly typical of all bud sports in that the mutation occurred too 
late in the development of the young shoot to change all the cells in the 
corm and so make all the flowers red. It was chosen first, because the 
mutant character is dominant,! which makes it certain that the sport 
was due to mutation rather than to segregation, and second, because 
it also illustrates the origin of chimeras. In many cases of discontinuous 
bud variation the entire shoot is affected. Cases of bud variation pre- 
sumably caused by factor mutations which condition manifold character 
differences are occasionally found in the citrous fruits. The so-called 
Australian Navel orange has undoubtedly arisen a number of times 
from the commerical variety, the Washington Navel orange, from which 
it differs in its propensity to rank vegetative growth combined with low 
productivity. Also the fruits are rough and of poor quality. Numerous 
other distinct types of oranges and lemons have been discovered, usually 
as a single tree or merely a branch on a tree of the commonly cultivated 
variety (see Fig. 161). 
A chimera is a mixture of genotypically diverse tissues in the same 
shoot. The nature, categories and artificial production of chimeras and 
graft hybrids are discussed in Chapter XXII. Here it is only necessary 
to point out that as they occur in nature they undoubtedly owe their 
origin to factor mutations. In the red and white flowered gladiolus 
an entire shoot became composite in nature through a factor mutation 
in a meristematic cell very early in the development of the stem. If 
the mutation had occurred later on at just the right point in the vegetative 
cone, it might have produced a single red and white flower. This is 
apparently the manner of origin of the odd stripes on certain fruits 
such as the lemon shown in Plate II. In this case it is evident that 
mutations occurred in two different cells. In one case the factor change 
resulted in the laying down of yellow pigment of a deeper shade (‘‘deep 
chrome,” No. 17b of Ridgway’s Color Standards) than that normal 
for the variety, which is lmon chrome. In the other case the mutation 
1G. colvillei is a hybrid between G. cardinalis, which has bright scarlet flowers and 
G. tristis, which has white or yellowish flowers. 
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