Seeds of Phaseolus vulgaris L. beans were collected at weekly intervals throughout maturation and examined by scanning electron microscopy (SEM). No major structural changes were observed on the surface of the seed coat during the seven week study period. A cross-sectional examination of the seed coat revealed a substantial increase in thickness of the parenchyma cell layer in young seeds followed by a dramatic decrease in thickness as the seed approached maturity. In the cotyledons, the diameter of the storage cells and starch granules increased over time, with distinct protein bodies becoming visible only in the later stages of maturity. An extensive vascular system responsible for rapid delivery of water and nutrients to the cotyledons was observed in both immature and mature beans.
Hughes, Joe S. and Swanson, Barry G.
"Microstructural Changes in Maturing Seeds of the Common Bean (Phaseolus vulgaris L.),"
2, Article 2.
Available at: http://digitalcommons.usu.edu/foodmicrostructure/vol4/iss2/2