Bauhaus-Universität Weimar

50 
Influence of 
mass-selec¬ 
tion. 
as starting points for new races cannot depend exclusively upon apparent 
morphological differences. 
In commenting upon the influence of mass-selection, in a case such as 
this, Nilsson-Ehle (42 p. 128) says: “Were a mass-selection of plants over 
125 c.m. in height to be made from this old mixed sort, plants from types 
which normally produce a short straw would be taken as would also those from 
types which normally produce a taller growth. The latter would naturally 
preponderate whereby a certain advance in the desired direction would likely 
be made.” It is quite possible, however, that an advance in one direction 
may be made at the expense of some more valuable quality, hence the 
danger which is associated with this form of selection. 
The Origin of Aberrant Forms as Quantitative Hereditary Variations. 
Apart from the mass of apparently related individuals which go to make 
up the greater part of a plant population, there may occasionally arise 
strange forms which at first sight do not seem traceable to any definite 
parentage. There may arise bearded heads of wheat in a bald sort, brown- 
chaffed individuals in a white-chaffed sort, white-kernelled forms in a red- 
kernelled sort, etc. In oats, white and grey kernelled individuals have been 
found in black-grained sorts and vice versa, while side oat types have been 
found in sorts characterized by spreading panicles. Formerly these aberrant 
forms were commonly regarded as Atavists or Reversions, being looked upon 
as the sudden reappearance of certain ancestral characters. More recently 
they have received the name Mutation. Experience at Svalöf and elsewhere 
has shown that the majority of these so-called novelties which thus suddenly 
appear in cultivated crops may be produced artificially by cross-hybridiza¬ 
tion and may therefore be regarded in most cases, simply as new combina¬ 
tions of already existing units. Apart from the great scientific interest which 
surrounds the appearance of these aberrant individuals there is an interest 
for the practical breeder which cannot be denied. If these forms represent 
mutations by which apparently new characters are suddenly acquired, it 
would clearly be the breeder’s main duty to watch carefully for their appear¬ 
ance in his fields with a view to isolating and propagating them and perchance 
obtaining something better than the old sort. On the other hand, if they 
represent the results of natural crossings between different sorts, as they are 
now believed to do, it is of much less importance to spend time in seeking for 
things which can be produced artificially with much greater assurance of 
obtaining an advance. Thus where formerly, striking natural crosses found 
in the experimental plots at Svalöf were eagerly isolated and studied they 
are now very largely ignored unless the marks by which they are characterized 
point to a certain parentage of known value. Instead it is preferred to make 
crossings artificially between known sorts whose values have already been 
proven.
        

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