Structure, Physical Characteristics, and Com- Position of the Pericarp and Integument of Johnson Grass Seed in Relation to Its Physiology 1
STRUCTURE, PHYSICAL CHARACTERISTICS, AND COM- POSITION OF THE PERICARP AND INTEGUMENT OF JOHNSON GRASS SEED IN RELATION TO ITS PHYSIOLOGY 1 By GEORGE T. HARRINGTON, formerly Scientific Assistant, Seed-Testing Laboratories, and WILLIAM CROCKER, formerly Plant Physiologist, Drug Plant, Poisonous Plant, Physiological and Fermentation Investigations, Bureau of Plant Industry, United States Department of Agriculture. INTRODUCTION These investigations were undertaken in hope of explaining some fea- tures of the behavior of Johnson grass seeds during their initial dormancy, their period of after-ripening, and their germination. As has been shown elsewhere (15) ,2 Johnson grass seeds belong to that group whose well- matured embryos are never'appreciably dormant, the dormancy of the intact fruit being imposed by its outer, nonliving structures. These include (1) the closely adhering, hard, brittle scales, (2) the fused pericarp and inner integument. Removal of the former hastens the germination and increases the germination capacity of the caryopses, whether these are freshly gathered, are fully after-ripened, or are in process of after- ripening, but does not appreciably affect the rate of after-ripening. Furthermore, removal of the fused pericarp and integument by corrosion with concentrated sulphuric acid or even its removal over one side of the embryo by means of a sharp needle induces the complete germination within three or four days even of freshly gathered grains which, without such treatment, would scarcely germinate at all in weeks or months. It has also been shown (15, 16) that the germination of Johnson grass seeds is highly dependent upon the maintenance of alternating temper- atures, that this sensitiveness to temperature conditions disappears upon the removal of the seed coverings, and that certain chemical substances exert a stimulating action upon their germination, particularly after the removal of the caryopses from the inclosing scales.
[Show full text]