Ultrastructural Observations on Aging of Stationary Cultures and Feeding in Ochromonas*

SYNOPSIS. Changes accompanying aging of stationary cultures of Ochromonas danica were examined with the electron microscope. The cultures included light‐ and dark‐grown populations ranging in age from 3 days to 5 weeks. Cells from the youngest cultures contained minimal amounts of lipid and a distinct leucosin vacuole. After 1 week, the number of lipid globules in the cytoplasm increased. The amount of lipid increased progressively in cells from older cultures until the leucosin vacuole was obliterated by the coalescing spheres. Cells from cultures older than 3 weeks showed a general breakdown of cytoplasmic integrity. An area of pinocytotic activity was also present; a relationship between this anterior region and blebs arising from the cell membrane is suggested.