20 GEORGE HARRISON SHULL 



under date Nov. 7, 1904: "Counted the rows on the ears of White dent corn 

 raised in Carnegie garden this year." In fact, as I think of it now, I doubt 

 that I could have bought white dent corn in the feed market of Long Island 

 at that time. 



I planted the Corry sweet corn on May 17. On July 18 I bagged the corn 

 preparatory to making crosses between the two varieties. This crossing was 

 carried out on the Corry sweet on July 25, and the crosses for the reciprocal 

 combination were made on July 27 and 28. These were the first controlled 

 pollinations I ever made in corn, and they were not part of a scientific ex- 

 periment. 



My interest in investigating the effects of cross- and self-fertilization in 

 maize arose incidentally in connection with a projected experiment with 

 evening primroses (Oenothera) to determine the effect, if any, of these two 

 types of breeding on the kinds and the frequencies of occurrence of mutations. 

 A critic of De Vries's mutation theory had urged that the mutations dis- 

 covered by De Vries in Oenothera lamarckiana were artifacts produced by 

 selfing a species which, in a natural state, had been always cross-fertilized. I 

 developed a program to put this question to a crucial test . Then, it occurred to 

 me that it would be interesting to run a parallel experiment to test the effects 

 of crossing and selfing on the expressions of a purely fluctuating character. 

 Since I had available this culture of white dent maize, I chose the grain-row 

 numbers on the ears of corn as appropriate material for such a study. The 

 Oenothera problems thus begun, continued to be a major interest throughout 

 my genetical career, but it is not expedient to pursue them further here. It is 

 important, however, to keep them in mind as a key to my motivation in 

 launching my studies with maize. 



In this double-barreled exploration of the genetical effects of cross-fertili- 

 zation versus self-fertilization, I had no preconception as to what the out- 

 come of these studies would be in either the mutational or the fluctuational 

 field. Certainly they involved no plan for the demonstration of distinctive 

 new biotypes, nor any thought of the possible economic advantages of either 

 method of breeding. I was a faithful advocate of the early biometricians' slo- 

 gan: Ignoramus, in hoc signo lahoremus. Until the middle of summer of 1907, 

 certainly, I had no premonition of the possible existence of a heterosis prin- 

 ciple which would have important significance either scientifically or eco- 

 nomically. I was forced to recognize this principle by direct observations of 

 manifestations in my cultures which had not been anticipated, and there- 

 fore could not have been planned for. 



Let us proceed then to a description of my experiments with corn which 

 forced the recognition of this important phenomenon. The culture of white 

 dent corn which we had growing, almost incidentally, on the Station grounds 

 that first year, showed no variations that seemed to indicate the presence of 

 any segregating characteristics. It appeared to be ideal material for the study 



