322 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



endosperm nucleus, which results from the fusing of the three nuclei, 

 is triploid, or has the 3n number of chromosomes or 30 ordinarily in 

 corn. Since all the cells of the endosperm tissue are descendants of 

 the triple-fusion nucleus, all the cells of the endosperm are triploid. 

 While this is occurring, another male gamete fuses with the egg. The 

 fertilized egg or zygote then is diploid or has the 2n number of chro- 

 mosomes, which in corn ordinarily is 20. By cell division the zygote 

 becomes an embryo, cA-ery cell of which is diploid, and as the growth, 

 including cell division, continues, maturity of the plant is attained, 

 with all the cells of the roots, stem, and leaves being descendants of 

 the fertilized egg, each having the diploid number of chromosomes. 



The corn endosperm (pi. 4, fig. 18, E) is noted for the great accumu- 

 lation of foods, carbohydrates, and protein. It is a basic food source 

 for many people, and has no equal as feed for farm animals. In 1952, 

 3,306,000,000 bushels grew on the farms of the United States. Numer- 

 ous genetic variations (pi. 5, fig. 21) occur in the endosperm as to kind 

 of carbohydrate, physical qualities, and pigmentation. In this illustra- 

 tion six fundamental endosperm types are shown on the ear — floury, 

 dent starchy, flint, sweet, waxy, and pop. Tlie floury type of endo- 

 sperm has a high percentage of starch in relation to the protein content, 

 is soft and readily ground by the primitive methods of the Indians, 

 and was a common variety with them. Our common field corn varieties 

 are of the dent starchy type. The flint type of endosperm is hard and 

 hornlike, and was cultivated extensively by the Indians. Sweet corn, 

 although known by the ancient Peruvians and by a few of the North 

 American Indians in the latter part of the eighteenth century, never 

 became important with them, and white man became interested in it 

 about a century ago. Waxy corn is characterized by the presence of a 

 waxy carbohydrate, erythrodextrin. Its culture history is uncertain. 

 The Indians apparently made no use of it. Geneticists in this century 

 found in it a useful tool in certain genetic studies and preserved stocks 

 for that purpose. When World War II came along, cutting off the 

 supply of cassava used in the manufacture of tapioca, a considerable 

 acreage of hybrid waxy corn developed, the erythrodextrin being used 

 in the making of tapioca and postage-stamp glue. Popcorn seeds have 

 a hard, horny endosperm which explodes when heated, forming the 

 white, soft, spongy mass of this popular confection. It was known and 

 used by the ancients of Mexico and Central America. 



Plate 5, figure 22, shows the results of crossing a pure-line red flint 

 plant with a pure white flint corn plant. The ears borne on the white 

 plant as a result of the cross pollination will be red-grained and the 

 embryo in every grain will be hybrid. "V^Hien these hybrid grains aie 

 planted and the mature hybrid plants are self-pollinated, the resulting 

 ears will show a segregation of three red grains to one white, a typical 



