Chromosomes in Hybrids between Euchlaena Perennis and Zea

Hybrids between maize (Zea mays L.) and perennial teosinte (EuMaena perennis Hitchc.) offer a favorable opportunity to follow the behavior of triplicate sets of chromosomes in a triploid hybrid. Maize, the diploid parent, has been carefully analyzed both genetically and cytologically. Perennial teosinte seems to be unquestionably a true tetraploid. Its tetraploid character is evident from (1) the prevalence of tetravalent chromosomes at diakinesis observed by Randolph ^ and by the writer; (2) the X-ray experiments of Randolph (17) j^ who obtained from the 20-chromosome annual Euchlaena a 40chromosome perennial plant very like E. perennis ] and (3) genetic studies which show that Fi teosinte-maize hybrids contain three sets of homologous chromosomes. Although extensive genetic studies were carried on in conjunction with the cytological studies, the present paper treats only of the chromosomes as found in Fi and later hybrid generations. The first plants of perennial teosinte were found in Mexico by Hitchcock in 1910 and were introduced into this country by Collins {4) in 1921. The first hybrid with maize was made early in 1922 by C. G. Marshall. The breeding has been done largely at the United States San Diego Acclimatization Garden at Torrey Pines, Calif., where the more promising perennial hybrid forms are maintained in permanent plantings. The methods of crossing have been similar to those used in corn-hybridizing studies, but to bring plants with very different flowering dates into flower at the same time, plantings were made at different seasons and late-flowering plants were frequently given an artificial short day. The cytological material, which had been collected just before the tassel emerged from the leaves, was put in Carnoy's killing fluid for half an hour; this fluid was then poured off and the material was covered with absolute alcohol. Material preserved in this way is generally satisfactory for the determination of chromosome numbers by the use of the acetocarmine smear method.