Dormant and Non-dormant Seeds: Similar Germination Responses when Osmotically Inhibited

Abstract

Chen and Thimann1 have ascribed photodormancy and thermodormancy in seeds to the effects of continuous irradiation and supraoptimal temperature on the balance between the “expansive force” of the embryo and the mechanical constraint of the enveloping tissues. Dormant seeds of Phacelia tanacetifolia were induced to germinate under these inhibitory conditions by cutting the radicular end of the seeds, an operation which reduced mechanical constraint. Inhibition of germination was reinstated in cut seeds by imbibition in an osmotic solution which reduced the expansive force of the embryo. The implication appeared to be that the responses to such experimental manipulations are restricted to naturally dormant seeds. The cause of variation in “expansive force” or “growth potential”2 as affected by radiation and temperature are apparently unknown, but the phenomenon can be demonstrated in non-dormant seeds of cultivated plants (Table 1). The seeds of these species are considered to be non-dormant because high percentages of germination can be obtained at any constant temperature within a wide range, in darkness or under periodic or continuous irradiation.