336 GENETICS IN RELATION TO AGRICULTURE 
An interesting illustration of what can be accomplished in maize 
merely by mass selection, when a definite ideal is maintained and seed 
is selected in the field before harvesting, is found in the Delta Farm White 
Corn shown in Fig. 136. 
Selection Methods in Breeding Close-pollinated Plants.—The suc- 
cessful methods of breeding wheat have been reviewed in preceding 
chapters. Compared with the methods required for corn the work of 
isolating genotypes in wheat is relatively simple. Most commercial 
7 
Fie. 137.—Typical heads from seven pure lines of Defiance wheat. Nos. 1 and 2 do 
not yield one grain per spikelet on the average; Nos. 6 and 7 yield from 4 to 7 grains per 
spikelet. Note tendency to club type in No. 6. 
varieties of wheat are a mixture of pure lines which can be isolated by 
single plant selections. In Fig. 137 is shown a typical head from each 
of 7 different pure lines isolated by selecting single plants from a plot of 
Defiance wheat. Nos. 1 and 2 did not have an average of one grain 
per spikelet while Nos. 6 and 7 bore from 4 to 7 grains per spikelet. If 
Nos. 6 and 7 prove to be superior in other characters also, they need only 
to be multiplied in order to yield greatly improved strains of the Defiance 
variety. It was by this method that Roberts in 1906 isolated a pure 
line of Turkey wheat that appears very promising for the Great Plains 
Region. It is worthy of note that this superior pure line was the 135th 
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