Color enhanced transmission electron micrograph of a plasma cell from guinea pig bone marrow. Some plasma cells do not concentrate their products in discrete secretory granules. In such cells, storage takes place within the cisternae (ribbon-like structures in green area) of the endoplasmic reticulum. Cisternae shown here are distended with protein. Other parts of the cell identified here include: euchromatin (bright red), heterochromatin (dark red), & mitochondria (dark blue).