B. P. I.— 668. 



CROSSBREnDING CORN. 



INTRODUCTION. 



In the United States corn has become the leading and most uni- 

 versally grown crop, perhaps more because of its natural adaptability 

 and productiveness than because of any improvement of the plant 

 intentionally accomplished by man. Human efforts have doubtless 

 had a great influence upon the evolution of maize, and it has been 

 modified so as better to meet human needs. These changes, how- 

 ever, have come about probably more because of the interdependent 

 relations that have existed between man and corn than through 

 knowledge intentionally applied. The evolutionary steps that have 

 developed the maize plant as it exists to-day are so little understood 

 that they are of little value in indicating methods to be adopted or 

 avoided in further improving this crop. Such improvement may 

 rest upon a close study of the effects upon the plant of different 

 methods of breeding and a correct application of the principles 

 evolved. 



The success of the work of the Office of Corn Investigations in 

 originating and improving high-yielding strains of corn for different 

 sections of the United States has been due to the utilization of the 

 effects of acclimatization, crossbreedmg, and selection. Of these 

 three factors crossbreeding is the principal one here under considera- 

 tion; but as these as well as other factors — such as seasonal and soil 

 conditions — usually operate together in influencing plant growth, 

 the effects of all factors that can not be elimmated must receive 

 consideration whenever comparisons are made. 



Because crossbreeding of corn is so readily accomplished, and the 

 results are so varied and interesting, and because crossbreedmg is so 

 generally recognized as a very important process in plant improve- 

 ment, the corn investigations of the Department of Agriculture 

 during 1900 and for several years following consisted very largely in 

 crossbreeding all types obtainable. Of the first-generation crosses 

 tested some were unusually productive, some good, some indifferent, 

 218 7 



