18 GEORGE HARRISON SHULL 



"The relation of certain biological principles to plant breeding," which was 

 published in 1907, only a few months before I read my paper in his presence 

 in Washington, D.C., what seems like an echo of the final conclusion of 

 Shamel, above cited. In this bulletin East urged that "corn breeders should 

 discard the idea of forcing improvement along paths where nothing has been 

 provided by nature," specifically rejecting a program of isolation of uniform 

 types because of a "fear of the dangers of inbreeding," adding that he was 

 "not able to give a reason for this belief beyond the common credence of the 

 detrimental effects of inbreeding." He returned to this problem of the de- 

 terioration due to inbreeding in his Annual Report to the Conn. Agr. Exp. 

 Sta. for 1907-8, prepared in 19C8, with my paper before him. In this report 

 he says: 



I thought that this deterioration was generally due to the establishment and enhance- 

 ment of poor qualities common to the strain. ... A recent paper by Dr. George H. Shull 

 ("The composition of a field of maize") has given, I believe, the correct interpretation of 

 this vexed question. His idea, although clearly and reasonably developed, was supported 

 by few data; but as my own experience and experiments of many others are most logically 

 interpreted in accordance with his conclusions, I wish here to discuss some corroboratory 

 evidence. 



We have thus far failed to recognize the existence of a general heterosis 

 concept among plant breeders, prior to the reading of my paper on "The 

 composition of a field of maize" in January, 1908, even when they were using 

 the methods of inbreeding and controlled crossing in which such a concept 

 could have developed. 1 must mention, however, a near approach to such a 

 concept from the side of the animal breeders. Before the American Breeders' 

 Association, meeting in Columbus, Ohio, 1907, Quintus I. Simpson, an ani- 

 mal breeder from Bear Creek Farm, Palmer, Illinois, read a paper which 

 definitely recognized hybridization as a potent source of major economic 

 gains beyond what could be secured from the pure breeds. The title of his 

 paper, "Rejuvenation by hybridization," is more suggestive of the views of 

 Thomas Andrew Knight than of the current students of heterosis, but the 

 distinction seems to me to be very tenuous indeed. 



Although I listened with great interest to Simpson's paper, I do not think 

 that I recognized any direct applications of his views to my results with 

 maize. I was working within the material of a single strain of a single species, 

 and not with the hybridizations between different well established breeds to 

 the superiority of whose hybrids Simpson called attention. 



Students may make varying estimates as to how closely the work of men 

 to whom I have referred approached the heterosis concept as we understand 

 it today. But there can be no doubt that there was a beginning of this concept 

 in the course of my own experiments with corn. At the beginning of 1907 I 

 had not the slightest inkling of such a concept. By the end of 1907 I had 

 written the paper that brought such concept clearly into recognition. At that 

 time I knew nothing of the work of Beal, Holden, Morrow and Gardner, 



