GENETICS — STERN 271 



the goal of homogeneity of one generation and increased immensely 

 its yield. For this increase it had to pay a price, the renunciation of 

 likeness of successive generations. The technique of raising hybrid 

 corn arose from a theoretically and experimentally inspired contem- 

 plation of the composition of a field of com as it used to be grown all 

 over the world. It became apparent that the varieties of corn then on 

 the market were far from being homogeneous. Wlien genetic proce- 

 dures were used to obtain pure lines they were successful. Many 

 different pure lines were produced, each one homogeneous within and 

 between generations— but none was of practical value. Always 

 growth was stunted, and fertility low. This appeared strange enough, 

 but stranger still, and happier, was the outcome of crosses between 

 the poor, pure lines. The hybrids not only showed better vigor than 

 their parents, but they surpassed the desirable qualities of the indi- 

 vidual members of the old field of corn. 



That the desirable crossbred plants were undesirable as producers 

 of seed for future generations lay in the nature of the genetic makeup 

 of the hybrids. The shuffling in reproduction of the parental genes 

 would result in renewed heterogeneity of the next generation, and in 

 loss of the specific hybrid vigor. Thus the discovery which had 

 yielded such desirable produce requires each year anew the effort of 

 hybridization of the, by themselves, undesirable pure strains. 



The theoretical problems of hybrid vigor are not yet solved. On 

 the contrary, the cause of this phenomenon is a matter of extensive 

 research at present. The practical fact is that after a slow start with 

 the first commercial seed field of hybrid corn grown in 1921, and a 

 gradual rise to 80,000 acres in 1932, now the greater part of the nearly 

 90,000,000 acres of field corn and sweet corn in the United States are 

 planted with hybrid corn. It has been estimated that perhaps a billion 

 bushels a year are now harvested in excess of the best national yields 

 we enjoyed before we had hybrid corn. 



Genetics is credited for this practical result because of the historical 

 fact that a pure geneticist, G. H. Shull, working at the Station for 

 Experimental Evolution on Long Island — not at an agricultural ex- 

 periment station — was the father of hybrid corn. Admittedly it was 

 no absolute internal necessity that the introduction of hybrid corn 

 into practice had to wait for the concepts of genetics. Indeed, the use 

 of crossbred field corn had been proposed many years earlier, while 

 mules, the vigorous but sterile hybrids of the horse and ass, had long 

 had a recognized place in animal production. Yet it seems that the 

 modern intellectual penetration into the phenomena of heredity was 

 required to rediscover, refine, and assure the acceptance of the uncon- 

 ventional procedure. 



The success of applied genetics with hybrid corn is followed closely 

 by the success of the breeder of disease-resistant wheat plants. Each 



