Scanning electron microscopy examination of soybean hilum development

Seeds of the soybean (Glycine max (L.) Merr.) cultivar Tracy-M were harvested from field-grown plants, and fractures of the hilum were examined with a scanning electron microscope. Macrosclereid and hilar fissure differentiation were observed at approximately 1% maximum seed size. The tracheid bar, stellate cells, sclerenchyma, and rim aril began differentiation near 5% maximum seed size. Outer integument differentiation was nearly completed by 35% maximum seed size, when articulated parenchyma, aerenchyma, and pits in the developing tracheids were observed. Hilum development was completed when the aleurone differentiated from the inner integument prior to seed maturity. Partial seed abscission was observed during hilum development.