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, 1 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 eariy 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. 176 of Ridgway's Color Standards) than that normal 

 for the variety, which is lemon chrome. In the other case the mutation 



1 G. colvillei is a hybrid between G. cardinalis, which has bright scarlet flowers and 

 G. tristis, which has white or yellowish flowers. 



