Preface 



Heterosis grew out of a desire on the part of Iowa State College to gather to- 

 gether research workers from marginal fields of science, each with something 

 to contribute to a discussion of a central problem of major national interest. 

 The problem of heterosis, as synonymous in large part with that of hybrid 

 vigor, formed a natural theme for discussion. As the reader will note, many 

 fields of science have contributed or stand to make significant contributions 

 to the subject. Major steps in the advance have led to divergent views which 

 may be rectified only through joint discussions followed by further research. 

 The conference of students of this problem was held June 15 to July 20, 1950. 



In furnishing the opportunity for these discussions by active research 

 workers in the field, Iowa State College hoped: to facilitate summarization 

 and clarification of the accumulated data on the subject, to encourage formu- 

 lation and interpretation of the observations in the light of present day bio- 

 logical information, to stimulate further advances in the controlled success- 

 ful utilization and understanding of the biological processes behind the phe- 

 nomenon of heterosis, and to increase the service rendered by this discovery 

 in expanding world food supply. 



Iowa has a direct, vested interest in heterosis. Today the agricultural 

 economy of the state is based upon hybrid corn. The scene portraying a hy- 

 bridization block of corn, shown here, is familiar to all who travel within the 

 state as well as to those in surrounding regions, for this method of corn 

 breeding has been shown to be surprisingly adaptable and useful in producing 

 more food per acre over wide areas of the world's agricultural lands. 



Iowa's indebtedness to heterosis, generated through crossing selected and 

 repeatedly tested inbred strains, is well known. Few outside the workers in the 

 field realize the full magnitude of this debt. 



With the progressive introduction of hybrid corn in 1936 there came a 

 steady increase in corn yields over both the former yields and over the 

 yields of other agricultural crops, as that of tame hay, which were not sub- 

 ject to this genetic method of yield improvement. It seems likely that in no 

 other period of like years has there been such an increase in food produced 

 over so many acres of land. The return from hybrid corn has been phenome- 

 nal, but it is now evidently approaching an asymptotic value. It behooves us 

 to find out as much as possible about the techniques and methods which 



