MUTATIONS IN PLANT BREEDING 369 
new characters. Surface and Zinn consider this sufficient evidence to 
make it ‘almost certain that similarly inherited variations may occur in 
respect to physiological characters such as yield.” That they were 
justified in making this inference is shown by the success of their ex- 
periments on pure line selections for yield. 
Other self-fertilized crop plants in which mutations have been reported 
are barley, wheat, tomato and potato. 
In maize the sudden appearance of new characters in established vari- 
eties or strains has been reported by a number of investigators. The 
remarkable diversity between inbred strains as discovered by Shull and 
by East indicates the extent to which germinal variations occur in this 
plant. Each author obtained one strain which was so nearly sterile as to 
be in danger of complete extinction while other strains appeared to be 
capable of maintaining fairly good annual yields indefinitely. Abundant 
evidence of the occurrence of factor mutations in maize is also found in the 
numerous pairs of contrasted characters which are inherited in Mendelian 
fashion. Besides those referred to in earlier chapters we may mention 
multiple stems (suckers) as dominant over single stems (no suckers), 
normal stature (tall) as dominant (usually) over dwarf stature, normal 
green leaves as dominant to striped leaves, presence and absence of aerial 
roots, hairy and glabrous stems, branched and unbranched tassel, normal 
ear and branched ear, normal anthers and fasciated anthers, presence of 
normal reproductive organs and absence of the same (barrenness). Most 
of these allelomorphs behave as unit characters. Various quantitative 
differences such as stature, ear-length and number of rows to the ear are 
either conditioned by several pairs of factors or by single pairs of factors 
which are subject to a wide range of variability in expression. Con- 
stitutional vigor and productivity are doubtless conditioned by the in- 
teraction of very many factors and a mutation in a single one would alter 
the end result. In short the inherent individuality of corn plants, which 
makes possible the successful application of selection methods, must be 
referred to factor mutations. 
Sugar beet improvement, particularly increase in sugar content 
of the roots, depends directly upon the occurrence and selection of 
mutations, according to Pritchard. As a result of statistical investiga- 
tions of variation, correlation, inheritance and selection in the sugar 
beet, he concludes that although sugar beet improvement has been ac- 
complished, continuous selection is not necessarily the determining 
factor in attaining the present high sugar content of the best varieties. 
His statistics show that the best roots transmit no better qualities 
than do the mediocre roots because the differences are merely “ fluctua- 
tions” (modifications). The real differences between sugar beet families 
are usually very slight and are greatly exceeded by their “fluctuations.” 
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