Structural and physiological observations on some small marine diatoms

Four new species of marine ultraplanktonic diatoms are described from observations with the light and electron microscopes. The requirements for vitamins and the responses to salinity and temperature were studied in axenic cultures. The relationship between physiological variability within a species and the environmental circumstances characterizing the habitats of different strains is discussed. We note the need for a study of infraspecific variability on both large and small geographic scales.