CELL ENLARGEMENT IN SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

Skeletonema costatum (Grev.) Cl. exhibits an asexual means, of increasing cell size that is more common than auxosporulation. This phenomenon accounts for the genetic stability of S. costatum in culture and for the deficiency of heterozygotes in natural populations, and has important implications far the life history of this species.