GENERAL PRELIMINARY STUDIES ON THE PHYSIOLOGY OF DELAYED GERMINATION IN AVENA FATUA

Abstract

A series of general preliminary studies was made on the physiology of delayed germination in Avena fatua, the results of which may be summarized as follows: (1) Great variations were found in the after-ripening periods of a number of A. fatua selections. (2) Evidence was obtained which strongly indicated that delayed germination is determined by a condition of the seed coat which develops after fertilization. (3) Results from tests of entire panicles indicated a correlation between germinability and the position of the seed in the panicle. (4) The after-ripening period of secondary grains was shown to be much longer than that of primary grains. (5) The placing of incompletely after-ripened grains under germinative conditions induced secondary dormancy. (6) Exposure to light appeared slightly to stimulate germination in seeds which were in the early stages of after-ripening, but appeared to have a harmful effect upon seeds which were more or less completely after-ripened. (7) Low dry-storage temperatures retarded the after-ripening process. Storage in a frozen condition at freezing temperatures resulted in increased germination. Seeds moistened and subjected to outdoor conditions failed to germinate. (8) Dormancy was more or less completely overcome by breaking the seed coat over the embryo, or by soaking seeds in potassium nitrate solutions. The exposure of seeds under germinative conditions to an atmosphere having an increased oxygen concentration definitely stimulated germination. Treatments with pure oxygen, ether, and sodium thiocyanate had more or less indifferent effects upon germination, while ethylene chlorhydrin and dichlorethylene were definitely injurious.It is inferred from the combined results that delayed germination is due to post-fertilization changes, related either to tissue absorption or development, which occur in the seed coats of A. fatua but not in readily germinable species, and which result in a restriction of the oxygen supply to the embryo. It is believed that the after-ripening process may consist, essentially, of a series of changes in the tissues of the seed coat which result in an increased permeability to oxygen.