RESULTS WITH HYBRIDIZATION 107 



HYBRIDIZATION, EFFECT ON GROWTH 



78. Two very distinct results follow cross-fertilization 

 in maize : first, certain hereditary characters from both 

 parents are bound up in the embryo, to be carried over 

 into the next generation ; second, a stimulus to vegetative 

 growth is given, to be carried over into the hybrid genera- 

 tion. The carrying over of hereditary characters has 

 already been discussed under the topics " Xenia " and 

 " Mendel's Law," and the principal discussion here will 

 deal with the second effect of hybridization. 



SELF-FERTILIZATION 



79. If a maize plant is self -fertilized (own pollen on own 

 silk), and this process is repeated for two or three genera- 

 tions, and selected seeds are used, there may gradually 

 be produced a " pure type." That is, the wide range of 

 variation is decreased each year, until the progeny of the 

 individual, being self-fertilized, are all of one type. For 

 example, ShuU self-fertilized corn plants of a white dent 

 variety for five years and, as a result, secured strains that 

 came true with 8, 10, or 12 rows, and so on up to 24-rowed 

 ears. The pure strains differed also in other respects, 

 but all the plants of a given pure strain were very similar. 

 At the Nebraska Agricultural Experiment Station ten 

 very distinct strains were isolated from Hogue's Yellow 

 Dent, by inbreeding for three years. 



The inbred strains also become dwarfish in size, have a 

 high percentage of barren plants, and sometimes become 

 entirely sterile. 



The decrease in yield is illustrated by the following data 

 from Shull. Two strains, designated as A and B, which 



