326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 4 



never simultaneously in all individuals in the population of a given 

 species. If one wishes to observe such variations, he must study indi- 

 viduals. The early horticulturist had incentive to observe and tend 

 individuals in his small garden, rather than large segments of a pop- 

 ulation, since he was dependent on the small patch for food. Any 

 variant that met his needs better was selected, protected, preserved, 

 and finally propagated. It was selected because it suited his purposes, 

 and without regard to the survival value of the plant growing in the 

 wild state. If good enough, from his standpoint, he would plant his 

 whole plot to the variant and eliminate the less desirable ancestral 

 type. Other members of his tribe planted it too, and eventually many 

 groups in a large area were culturing the new and desirable variant. 

 Additional variations occurred from time to time and were allowed 

 to accumulate. Eventually the accumulated heritable differences were 

 so great that the wild ancestor was no longer recognized. This is the 

 case with a large number of domesticated plant species from both the 

 Eastern and Western Hemispheres, such as the garden pea, rice, 

 potato, and tobacco, with maize or corn as the crowning example. 



The wild ancestor of corn is unknown. It has either become extinct, 

 or is so different in appearance that it has not yet been recognized. 

 There is some evidence that pod corn was cultivated by the Cochise 

 Indians of Arizona about 3,000 years ago (pi. 5, fig. 24). Pod corn 

 differs from ordinary maize in that each grain on the ear is enclosed 

 in a husk (bracts of the spikelet bearing the grain) . The pod charac- 

 ter is controlled by a single dominant gene. Some have regarded this 

 as being the original wild corn. This notion has been questioned, since 

 pod corn is no more able to survive in nature, without the aid of man, 

 than is ordinary corn. The pod chai'acter is readily transmitted to 

 any other variety of corn by cross pollination, resulting in a new com- 

 bination or a recombination of characters. A similar case was men- 

 tioned earlier in which white flint corn was crossed with red flint. Any 

 of the many varieties of corn will readily cross. Tliis hybridization 

 went on in gardens of primitive man, and undoubtedly occurred more 

 rapidly than in the wild state because of the greater concentration of 

 plants. 



In some plants (maize being the outstanding example) the hybrid 

 (heterozygous) individuals are more vigorous than either of the 

 parents. Man was unaware of this hybrid vigor (heterosis) until 

 Shull discovered it in 1908 and 1909. This discovery was not put to 

 practical use for almost 25 years. Now, about 90 percent of corn 

 acreage is hybrid. The use of hybrid seed for planting may result in 

 an increase in yield of as much as 25 percent. This ranks as one of 

 the greatest achievements in plant breeding. 



Some place in the area from Mexico to Honduras, in the pre-Colum- 

 bian period, there is evidence that maize crossed with the gamma grass 



