340 GENETICS IN RELATION TO AGRICULTURE 
says, “the indications are that from a practical breeder’s standpoint 
permanent improvement in pure lines in small grains, if possible, is 
certainly not rapid or apt to be very marked.” He also suggests that 
much more rapid progress could be made by isolating pure lines from 
mixed populations and combining the desirable characters of these lines 
by hybridization. 
Other crops in which the method of selecting pure lines is applicable 
are oats, barley, peas and beans. Notable improvement has been made 
in oats by this method at the Svaléf, Cornell University and Maine 
Experiment Stations. The general method of procedure at the Maine 
Station is indicated by Surface and Zinn in their bulletin on pure line 
varieties of oats (see p. 371). The pure lines finally retained came 
from only three varieties, viz., Banner, Irish Victor and Imported Scotch. 
It is noteworthy and consistent with Mendelian principles that the 
physiological characters which result in higher yield are not necessarily 
associated with morphological characters in the plant or grain. Similar 
results with winter-resistant barleys have been reported by Spragg of 
the Michigan Station. The practical importance of the selection of 
pure lines as one phase of a complete system of breeding as practised 
with autogamous species is given further attention in Chapter XXI. 
Selection which is to result in the isolation of the most superior 
genotypes must begin with individual plants. In dicecious and self- 
sterile plants this method is inapplicable. Here the breeder must begin 
with phenotypically similar individuals and continue inbreeding of simi- 
lar plants for several generations in order to isolate approximately uniform 
strains. The earlier improvement of the sugar beet was accomplished 
by mass selection. But in recent years the producers of commercial 
seed have introduced a system of line selection. According to Briem, 
reliable seeds cannot be obtained by selection in the lump, nor from a 
single generation of mother beets followed by the cultivation of seed roots. 
An individual selection must be made the characteristics of which are 
assured by testing for three generations. That is to say, since the beet 
is a biennial 6 years are required to obtain seed of guaranteed quality 
for the seed roots and another 2 years must pass before the market 
product is ready. Briem’s opinion is in harmony with Pritchard’s con- 
clusion that continuous selection is not an efficient method of sugar beet 
improvement and that the improvement of the past is the result of 
isolating mutations (see p. 369). 
In emphasizing the importance of finding the best genotypes within 
a chosen species or variety the usefulness of mass selection should not be 
overlooked. It is frequently the first or only practicable step to take in 
purifying a commercial variety. The so-called “running-out”’ of varie- 
ties can be prevented by reasonable care to avoid mixing seed and by occa- 
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