302 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



cal domination in Eussia. The curbing of the spread of communism in 

 western Europe after the more recent World War may in a very consid- 

 erable measure have been due to the boon of hybrid corn, as Paul Man- 

 gelsdorf of Harvard University has claimed. 



It is of some interest, therefore, to see just what G. H. Shull did with 

 his corn plants. He started out with the intention of studying the in- 

 heritance of quantitative characters, such as yield, in order to see 

 whether these followed the laws of Mendelian inheritance; and he 

 began by inbreeding his lines. He found that this inbreeding brought 

 out a number of hidden, deleterious hereditary characteristics, and that 

 the inbred strains showed a marked loss of both vigor and productive- 

 ness. Eventually he obtained very pure strains of great uniformity, 

 though for the farmer totally worthless, runty, and weak, with small 

 ears bearing few seeds, and of course very low in yield. When, how- 

 ever, two of these inbred lines were crossed together, there was a phe- 

 nomenal improvement in the hybrids. The ears were large and full, 

 and the production equaled or bettered that of the best strains of the 

 time. 



In 1917 Donald F. Jones, at the Connecticut Agricultural Experi- 

 ment Station, invented the so-called "double cross," with quite the op- 

 posite effect from that of the usual connotation. By crossing together 

 the two hybrids produced from the single crosses of four different 

 inbred lines, a, b, c, and d, Jones obtained seed that, when planted, con- 

 siderably exceeded in vigor and yield even the hybrids of the first 

 crosses, of a with b, and of c with d. Seed produced by Jones' method 

 is the present-day hybrid corn, and later efforts have been devoted 

 simply to finding the best inbred lines to combine for a particular pur- 

 pose or area, and to producing the hybrid seed in a quantity great 

 enough to plant some 60 million acres. 



The same hybrid corn that is best suited for growth in Iowa is not 

 adapted to Texas, and assuredly not to Mexico. Hence the extension of 

 the benefits of hybrid corn to the entire Nation, and then to foreign 

 countries, requires a repetition of the process while utilizing native 

 strains of maize. This takes time, but requires no essential modifica- 

 tion of theory or method. Already in Mexico hybrid com suited to the 

 country has been produced and is revolutionizing the agriculture of 

 that country, and with it the level of well-being and the culture of the 

 people, which from pre-Conquest days has been based on maize. When 

 we realize that today two-thirds of the world's population are chroni- 

 cally malnourished, and that larger and larger populations are inevi- 

 table before the world population can be stabilized, the importance of 

 hybrid corn and similar products of the geneticist's plant breeding 

 becomes fully evident. 



Eventually we may have to subsist on great quantities of yeast or 

 some microscopic alga like Chlorella that can be raised by the ton in 



