GENERAL CONSTDEEATTON OF ATJ. TTIE TESTS. 67 



variety advantageously and some disadvantagcously, tliough in 

 general there is a tendency for the difl'erent ears of a variety to 

 respond similarly to the crossing. Another line of work being con- 

 ducted by the Office of Corn Investigations indicates that what has 

 just been said about the crossing of one variety with another also 

 applies to the crossbreeding of individual plants within a variety. 

 Just as certain pairs of varieties combine or nick advantageously, 

 while other pairs nick disadvantagcously, so some pairs of individual 

 plants nick advantageously, while other pairs nick disadvantagcously. 

 Tliis shows the results obtained by crossing two varieties without 

 reference to individual plants to be but an average of the results 

 that would be obtained by crossing many individual plants of those 

 varieties. The average results may be an improvement over either 

 parent and still fall short of what could be obtained by restricting 

 the crossing to the individuals that nick most advantageously. 



In connection with this consideration of crossbreeding, it is inter- 

 esting to note that such varieties as Selection 119, Selection 160, and 

 Chisholm, wliich are among the most profitable varieties for their 

 respective localities, have not been crossbred or mixed with other 

 varieties for liiany years. The same can be said of leading strains of 

 corn of other localities, and their merits are doubtless largely due to 

 effects of selection, acclimatization, and adaptation. 



The results of these tests show that with corn some first-generation 

 crosses are more productive than either parent, that some are inter- 

 mediate between the two parents in productiveness, and that some 

 are less productive than either parent. They also show that the 

 determination of the particular first-generation crosses that can be 

 most profitably grown is attended with so many complexities that 

 careful tests must be made in a locality before the farmers of that 

 locality can be intelUgently advised whether it is to their interest to 

 continue planting a pure-bred strain, or to plant a first-generation 

 cross of certain strains. 



In crossbreeding corn for practical results it seems the duty of 

 State experiment stations and of corn breeders to determine what 

 two varieties nick to best advantage in producing seed for different 

 environments. Whether the yearly production of a particular first- 

 generation cross will be found advisable, or whether its use in making 

 other crosses will be found more profitable, must be estabhshed 

 by further work, and perhaps for each individual case. Progress in 

 producing higher yielding strains of corn depends upon the proper 

 combination and application of the effects of acclimatization, adapta- 

 tion, crossbreeding, and selection. 



218 



