GENERAL CONSIDERATIONS AND CONCLUSIONS 441 
operations of breeding result in “new creations” in the sense of bringing 
new characters into existence outside of those already attained in the 
course of evolution. Moreover, it would be very difficult to maintain a 
distinction between conservation and construction in modern breeding. 
A scientifically planned system of breeding improved crop plants must 
be founded upon suitable methods of testing the species, varieties and 
biotypes available in order to discover the most promising material 
for the constructive work of the hybridist. 
Uneconomical methods must be eliminated. There are sources of 
enormous waste in present day plant breeding work. An example is 
the useless attempt at improving pure lines through continual selection; 
another is the assumption that a single pure line selection represents all 
there is in a variety, a serious mistake since most commercial varieties 
of self-fertilized plants consist of a mixture of pure lines. The frequency 
of mutations in all economic plants has a direct bearing upon these ques- 
tions of breeding practice; hence this is a subject which deserves more 
thorough investigation. The evidence in some species is rather definite, 
however. In the potato, for example, it is probable that bud mutations 
are very, very rare. Yet the idea still prevails that disease resistant 
strains of commercial varieties of potatoes can be obtained by hill selection 
methods. In a variety susceptible to a given disease such strains would 
have to originate as bud mutations and, while it is possible of course that 
such a mutation in a given variety might occur, still in the light of what 
is now known about the rarity of bud mutations in the potato it is prob- 
able that in order to locate such a strain it would be necessary to test 
millions of plants under conditions favorable for the disease. Severe 
epidemics occasionally furnish opportunity for such selection on a grand 
scale. But the scientific plan of procedure is to undertake variety test- 
ing on a large scale preparatory to hybridization of the most promising 
forms. 
The matter of adjustment between varieties and local environmental 
conditions is of considerable importance. This is more widely recognized 
in cotton perhaps than in any other crop. Cotton growers are generally 
advised to secure locally grown seed, provided it has been properly selected 
and handled. Unless recourse is had to the production of Ff, hybrid 
seed, this consideration of adaptation to local environment is destined to 
become increasingly important as greater improvement is sought through 
more intensive selection. For this reason seed production will probably 
become more localized even though the business of handling and retailing 
remains in the hands of comparatively few commercial establishments. 
The recent rapid development and localization of truck crops in the 
United States as reported by Blair is a case in point. Specialization 
of this sort is bound to increase along with increase in population and 
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