Some Taxonomic and Ecological Considerations of Morphological Variation within Natural Populations of Benthic Diatoms Considérations taxonomiques et écologiques sur les variations morphologiques de diatomées benthiques en populations naturelles

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