Datensatz

Zusammenfassung

Deviation from typical valve outline has been used as a criterion for the erection of varieties of many naviculoid species, with or without consideration of the sizes of the observed valves. Yet valve outline is a feature which can change during succeeding generations of vegetatively dividing diatoms, smaller cells not necessarily being geometrically identical to larger ones. If a gradual change in shape occurs with reduction in cell size in nature a seasonal succession of morphological types is possible, while sampling frequency may determine whether or not these are recognised as stages in a continuum or as discrete entities.