CHAPTER VIII 



BUD VARIATION 



The outstanding feature of bud variation is that we know very 

 little about it. It is true that quite a number of cases of bud 

 variation have been investigated, but it could hardly be said that 

 altogether satisfactory explanations of the phenomena have as yet 

 been provided. The relation between bud variation and the 

 JVIendelian mechanism is difficult to visualize with much clearness, 

 nor is it easy to interpret the various cases in terms of each other. 



Bud variation may be defined as variation originating in vege- 

 tative tissue. Such variation might involve merely (i) 'fluctua- 

 tion," a response to environmental stimulus, or it might involve 

 (2) a change in the genetic constitution of the parts affected. 

 Cases of type (i) need not concern us here, since such variations 

 are not inherited. As for type (2), this should be subdivided into: 

 (a) cases in which the variation involves both somatic and germinal 

 tissue, and in which, therefore, the variation will be heritable 

 through seed; and (b) cases in which the variation involves somatic 

 tissue alone, the variation not being heritable through seed. With 

 these distinctions in mind, we may consider a classification of the 

 phenomena of bud variation, which is based primarily upon the 

 ideas of Emerson (6). 



I. SOMATIC MUTATION OF GENES 



This may be illustrated by some of the findings of Emerson 

 in corn. An illustration of variation involving both somatic and 

 germinal tissue is provided by the behavior of pericarp color. 5 

 is a gene which results in self- (completely) colored grains, being 

 dominant to V which produces variegated grains, and which in 

 turn is dominant to W which produces colorless grains. (These 

 are three members of a series of "multiple allelomorphs"; see 

 p. 112.) Corn of the formula VW, and which should, therefore, 

 have all the grains variegated, will at times have some grains that 



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