378 Inbreeding , Selection, and Heterosis 



This method has been used in a number of plants and has 

 produced some very valuable results. For years it was the 

 only method of improving maize by breeding and was probably 

 practiced by corn growers from the earliest times until just 

 a few years ago, when it was largely replaced by the method 

 of hybrid corn. One of the most active periods of selection in 

 maize was about one hundred years ago, and some of the corn 

 breeders of that era were masters at mass selection, which is 

 probably more of an art than a science. It has been suggested 

 that when mass selection is based both upon the phenotypic 

 quality of the plants used for seed and upon the performance 

 of the offspring, it is perhaps the best method of maintaining 

 the yield of varieties adapted to a given region in a cross-pol- 

 linated plant such as maize. Mass selection has been known as 

 the ^'German method" or the "German method of broad breed- 

 ing" because it was widely used at one time in Germany for 

 improving sugar beets and small grains such as rye and wheat. 



Line selection in a plant that normally is self-pollinated re- 

 sults in the isolation of pure lines or homozygous biotypes more 

 rapidly than any other method. In an animal or in a plant that 

 is normally cross-pollinated the result is slower, but it can be 

 produced by a suitable selection of male and female parents. 

 In many selection experiments, however, the female parent only 

 was considered and no attention was paid to the male. This 

 method, known as maternal-line selection, has produced some 

 very striking results in some experiments. 



One of the first maternal-line selection experiments was insti- 

 tuted by C. G. Hopkins a number of years ago at the Illinois 

 Agricultural Experiment Station. Selection was for high and 

 low oil content and for high and low protein content in the 

 kernels of maize. East points out that this work illustrates the 

 "rapidity with which progress can be made by selecting only 

 from the maternal side, even in the face of constant intercross- 

 ing." The work was started in 1896 from a very old type. 

 Burr's White. The method of selecting seed was known as the 

 ear-to-row method. 



Some of the kernels from an ear are planted in one row, 

 and the yield is later determined for the plants of that row. A 

 number of rows are grown, each of which has come from part 

 of a different ear. Either seed is selected for the next year's 



