MAIZE BREEDING 205 



of its characters. Fi crosses are of value from the standpoint of 

 earliness. Thus a cross, studied at Minnesota in 1919, between 

 Squaw flint and Minnesota No. 13, approached the dent parent 

 in height of plant and the flint parent in earliness and exceeded 

 both in yield. Such a cross would be of much value as a silage 

 or husking variety under northern conditions. 



The production of crossed seed is not very difficult. The va- 

 rieties to be crossed may be planted in alternate rows and the 

 tassels removed from one variety before any of the pollen has 

 matured. Seed produced by the detasseled variety is known 

 as first generation crossed seed. If the varieties to be crossed 

 differ in maturity they should be planted at different times so 

 that both bloom at about the same date. 



Isolation of Homozygous Strains. Shull (1908, 1909) first 

 suggested the utilization of crosses between self-fertilized strains 

 as a means of increasing yield in corn. Such crosses often give 

 very high yields. The chief objections to this method are that 

 self-fertilized strains are usually of very low yielding capabilities 

 and that the seeds from self ed lines are usually much smaller than 

 from normally pollinated corn. Even though crosses between 

 self -fertilized lines yielded very vigorously, the method has not 

 seemed commercially desirable. Low yields of seed per acre 

 would increase the cost of seed. Under unfavorable conditions 

 the food supply of the seed might not give the young F plant a 

 vigorous start. Jones (1918) has made a suggestion which 

 removes some of these objections. After isolating selfed strains, 

 tests are made to determine which four biotypes are most desir- 

 able as parents. Suppose these are numbered 1, 2, 3, and 4 

 respectively. Numbers 1 and 2 are crossed, also 3 and 4, by 

 detasseling all of one biotype in each group. Seed from the 

 plants of each detasseled biotype is then planted in alternate 

 rows in an isolated plot and all of one combination, as 3 X 4, 

 detasseled. Seed from these detasseled rows is used for com- 

 mercial planting. 



This method seems worthy of more extensive trial. Such a 

 cross was compared at the Connecticut station with the best 

 dent variety obtained from a varietal survey followed by a vari- 

 ety test. The highest yielding dent variety gave a yield of 92 bu. 

 while the cross under similar conditions yielded 112 bu. 



Every investigator who has produced self-fertilized strains of 

 corn has been impressed by the large number of undesirable 



