The Triradiate and other Forms of Nitzschia Closterium (Ehrenberg) Wm. Smith, Forma Minutissima of Allen and Nelson

Author:

Wilson Douglas P.

Abstract

1. The natural history in culture of the species of Nitzschia originally isolated from the sea by Allen & Nelson (1910) and grown at Plymouth and elsewhere ever since has been studied. It is shown that three main types of cell exist: normal with two arms (rostra), triradiate with three arms and ovals with none. Both normals and triradiates produce ovals by division, and the ovals so produced can multiply to form further ovals, or can grow either two or three arms, generally two, to form normal or triradiate cells.2. Ovals are more readily produced under good lighting conditions than under weak illumination.3. The cell wall is very lightly silicified, and the cells, unlike those of most diatoms, can elongate without auxospore formation. The maximum, and with it apparently the average, cell size of successive subcultures is variable.4. When triradiates are present they may, and frequently do under good cultural conditions, multiply faster than normal cells and finally may almost completely dominate the cultures. Now and again a proportion of the triradiate cells shorten one arm and gradually pass, during successive divisions, into the normal condition. There is a greater tendency for this process to take place in the autumn than at any other time. There was a notable instance in November 1941 when several cultures at Plymouth and at Hull simultaneously produced normals by this method on an extensive scale.5. There is evidence that under unfavourable cultural conditions triradiates tend to be eliminated.6. A cruciform type of cell has appeared occasionally in several cultures, but it has not been possible to obtain pure cultures of it, for the type appears to be somewhat unstable and readily reverts to the other forms. It has, however, persisted for a long time and for very many generations.7. It is shown that the triradiate type occurs in nature, and there is no reason to suppose that it is an abnormal form due to culturing.8. The nomenclature is discussed and it has been decided for the time being to retain the name Allen and Nelson originally gave to it, although there is a possibility that it is a species separate from Nitzschia closterium (Ehr.) W. Smith.

Publisher

Cambridge University Press (CUP)

Subject

Aquatic Science

Reference28 articles.

1. Peragallo H. & Peragallo M. , 1897–1908. Diatome'es marines de France et des districts maritimes voisins.

2. Ecological investigations with the continuous plankton recorder: the phytoplankton in the southern North Sea, 1932–37.;Lucas;Hull Bull. Mar. Ecol.,1940

3. Die Gattung Centronella Voigt.;Krieger;Ber. Deutsch. Bot. Ges.,1927

4. Die Kieselalgen.;Hustedt;Rabenhorst's Kryptogamen-Flora,1930

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