12 CONWAY ZIRKLE 



follow selfing, (2) that crossing imparts vigor, (3) that it is impossible 

 to tell in advance what varieties will produce corn of increased size when 

 crossed, (4) that what appears to be the best ear does not always produce 

 the largest crops, and (5) nearly all of the hybrid corn grown a second year is 

 smaller than that grown the first year, though most of it is yet larger than 

 the average size of the parent varieties. 



McClure also called attention to the fact that our fine varieties of fruits 

 have to be propagated vegetatively, and hinted that the deteriorations of 

 the seedlings from fruit trees was not unrelated to a like deterioration which 

 occurred in the seedlings grown from hybrid corn. 



The year following McClure's publication. Morrow and Gardiner (1893) 

 recorded some very pertinent facts they had discovered as a result of their 

 field experiments with corn. They reported that, "In every instance the 

 yield from the cross is greater than the average from the parent varieties: 

 the average increase per acre from the five crosses [they had made] being 

 nine and a half bushels." They noted further in a paper published later the 

 same year that, "It seems that cross bred corn gives larger yields at least 

 for the first and second years after crossing than an average of the parent 

 varieties, but how long this greater fruitfulness will last is undetermined." 

 Gardiner continued the work and in 1895 published the data he obtained 

 by repeating the experiments. He found that in four of six cases the yield 

 was greater in the cross, the average being twelve bushels per acre. 



We now come to the great corn breeding research project which was 

 undertaken at the University of Illinois in 1895 by Eugene Davenport 

 and P. G. Holden. Both of these scientists had been students of Beal and 

 were interested in his work on inbreeding and cross breeding maize. We 

 are indebted to Professor Holden for an account of this work which he printed 

 privately in 1948. This account gives us valuable historic data not to be 

 found elsewhere, as most of the University of Illinois records were destroyed 

 by fire. 



An intensive series of inbreeding experiments was undertaken by Holden, 

 and later on the inbred lines were crossed. Hybrid vigor was noted, and it 

 was found in addition that the crosses between different inbred lines differed 

 widely in their yield and in their general desirability. The main purpose of 

 the experiments was to find out how to use controlled crossing early and 

 effectively. After Holden left Illinois in 1900, the project was taken over by 

 C. G. Hopkins, a chemist, who was interested in increasing the protein con- 

 tent of maize. He hired as his assistant in 1900 a young chemist named 

 Edward Murray East, whom we shall hear about later. 



Our account of the background of heterosis is coming to an end as the 

 beginning of the twentieth century makes a logical stopping point. We should 

 mention, however, the great hybrid vigor discovered by Webber (1900) 

 when he crossed a Peruvian corn, Cuzco, with a native variety, Hickory 



