Excerpts from the report: Since its beginning, wheat has undergone many changes and now accounts for over 20 percent of the world's cropland and is grown in nearly every country. For years, any improvement in the wheat plant came about through selection of the best grain from one year's harvest as seed for the next year's plantings. However, since the early 1900's, plant scientists have been producing new varieties of wheat by genetic breeding. Only three species of wheat are commercially important in the world today and they account for 90 percent of all the wheat grown. These three species are Triticum aestivum (common wheat), Triticum compactum (club) and Triticum durum (durum). Wheat also may be further classified according to texture of the ripened kernel, color of the kernel, and the growing habits of the plant. Each of the 223 varieties grown in the United States may be classified under these three general features.