ABSTRACT
The majority of cells, whether animal or plant, protistan, fungal, or bacterial, possess an extracellular covering outside the plasma membrane. Cells apparently without a covering are relatively uncommon, and within the algae are limited to groupings such as the Pedinophyceae1 or occur as a stage in the life history of an otherwise cell wall-bearing organism, as, for instance, the gametes and zoospores of many green and brown algae.
