Corn-Makers 231 



that day. It was a full thirty years after the publication of his 

 findings that three other scientists, all of them working inde- 

 pendently, arrived at the same conviction which Mendel had 

 proved and then discovered among the archives in Brno, 

 Mendel's report which confirmed their own. 



Mendel had conducted his experiments almost entirely 

 with peas. Two of the later scientists, De Vries and Correns, 

 worked out their conclusions from experiments with zea mays. 

 American corn led to the re-discovery of the Mendelian law. 

 It proved to the satisfaction of the entire world that heredity 

 operates by a mathematical rule which is as true for mice as 

 for men, for the corn as for the pea. 



The acceptance of Mendel's law advanced the science of 

 genetics a full half century. American corn-makers, working in 

 various experiment stations, used it as a starting point for the 

 development of new and improved varieties of zea mays. One 

 of them, G. H. Shull, working at the Carnegie Institute's Sta- 

 tion for Experimental Evolution at Cold Spring Harbor, Long 

 Island, began to inbreed corn. His original aim was to study 

 the inheritance of the number of rows of kernels on the ears 

 as influenced by cross-pollination and self-pollination. His 

 experiments led to an entirely new method of corn breeding, 

 and to the creation of the first hybrid corn. 



Actually, what Shull, and after him innumerable other corn- 

 makers, did, was to inbreed certain selected lines for four and 

 five generations, thus intensifying their peculiar characteristics. 

 The seed of these inbred corns was not nearly so prolific as 

 other cross-pollinated varieties. But the experimenters were 

 not looking for fertility of seed. They were interested in in- 

 tensifying the hereditary characteristics of the chosen strains. 

 After four or five generations, two inbred strains were crossed. 

 The seed so produced had the vitality of a released prisoner, 

 greatly in excess of that of either of the two parent stocks, 

 even before the inbreeding was done. It had also the char- 

 acteristics of the two parent lines to a marked degree. 



In hybridizing corn it has been found that a "single cross" 



