Fig.
3.6-1. Section of bean cotyledon. These are storage
parenchyma cells in a germinating bean seed, storing both starch
grains (stained pink) and protein (colorless round or angular particles). The
very dark red bodies are nucleoli, and in several cells, the nuclei are visible
as a gray mass surrounding the nucleoli. These storage cells remain alive after
they have filled themselves, and they will be active in unloading the stored
carbohydrates and proteins as the seed germinates. In many monocots like corn,
wheat and rice, the storage parenchyma cells die after they have filled
themselves, and all unloading is carried out by enzymes secreted by other cells.
Many of the walls are indistinct in this section, having taken up only a little
of the stain, but where the walls are distinguishable, they are thin.