GERMINATION OF LIGHT-INHIBITED SEED OF NEMOPHILA INSIGNIS

Germination of Nemophila insignis seed is inhibited by light over a wide range of temperatures. At low temperatures the light intensity required for inhibition is higher. At 25 C there is little germination (in darkness as well as in light); at 27.5 C germination is inhibited altogether. Virtually complete germination in light is obtained when the endosperm directly covering the radicle is removed. This operation also improves germination in darkness at 25 C. Mechanical scarification performed elsewhere in the seed is without effect. As with Phacelia tanacetifolia, Nemophila seed apparently fails to germinate in light because the endosperm restrains the expansive growth of the embryo. The embryo of dark-imbibed seed develops a force which enables it to overcome the physical resistance of the endosperm. Light inhibits the process which leads to generation of “expansive force.” Gibberellic acid at 5 × 10^–4 m stimulates germination in light and in the dark. Abscisic acid at 10^-4 m inhibits germination; at 10^-6 m it inhibits only root growth. The inhibition of germination or root growth caused by abscisic acid cannot be reversed by gibberellic acid. Eighty per cent oxygen under certain conditions promotes germination. The rate of O₂ uptake is enhanced in oxygen-enriched atmosphere; however, there is no corresponding increase in the rate of CO₂ output. Thus high oxygen tension enhances an oxidative process other than respiration. This reaction is favorable to seed germination.