MUTATIONS IN PLANT BREEDING 371 
which gave rise to existing varieties. Factor mutations conform in 
their manner of occurrence with de Vries’ mutation theory; they arise 
suddenly, they occur in all directions, they are heritable, and some of 
them are advantageous to the species and are preserved by natural 
selection. When so preserved they give rise to new forms or races, and 
when fostered by man they make possible new horticultural varieties of 
plants or new breeds of animals. But as yet we have no ground for 
asserting that factor mutations are caused by geographical differences 
or by any specific elements of the environment. From his study of varia- 
tion in tobacco Hayes reached the conclusion that while environment is 
of great importance in breeding tobacco as well as in growing the commer- 
cial product, yet change of environment ‘‘does not cause a breaking up of 
type, and whatever variations occur due to environment appear alike in all 
plants of a particular type.”” Thus it appears that mutations arise quite 
independently of conditions of culture, and it is probable that they are 
somewhat more frequent than has generally been supposed. It is certain 
that mutations which are undesirable for agricultural purposes are quite 
as apt to occur as are desirable ones. For this reason neglect of seed selec- 
tion has caused the “‘running out’”’ of many good varieties. The breeder 
who would improve the best existing varieties which are adapted to a 
given location must either resort to hybridization between the varieties or 
else search for the most desirable biotypes within each variety. Even 
though hybridization is clearly necessary from the first, it may well be 
preceded by a systematic search for the best forms within the varieties to 
be crossed. 
One of the most successful attempts to take advantage of the desirable 
mutations which had occurred within cultivated varieties was carried out 
by Surface and Zinn at the Maine Experiment Station in their experi- 
ments on oat breeding. Oats being self-fertilized, they assumed that 
any new characters which had originated would breed true. The two 
most desirable improvements in the commercial varieties of oats culti- 
vated in Maine are increase in yield and in strength of straw. Accord- 
ingly individual oat plants were selected with these two points in mind. 
This work began in 1910 when 460 plants were chosen from 18 different 
commercial varieties. Of these only 188 were selected for planting in 
1911 and on the basis of the results obtained 80 were continued for test- 
ing in duplicate 1-2000 acre plots in 1912. Of these pure lines 34 were 
sufficiently promising to be continued into field tests in 1913. Thirty- 
‘one of these were again tested in 1914. In 1915 all of these pure lines 
were discarded except 12 and these were tested in quadruplicate plots in 
1915. In each of the 3 years 1913-15 these pure lines were grown along 
with a number of the best commercial varieties obtainable. In 1914-15 
the pure line plots alternated in the field with commercial variety plots. 
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