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Abstract
Sexual reproduction and auxospore development are described for a marine species of Bacillariaceae related to Nitzschia reversa. Oogamy, recently claimed to occur in N. pungens f. multiseries, was not found. No copulation envelope is produced and reproduction is isogamous. The orientations of the auxospores and gametangia bear no fixed relation to each other. A similar mode of auxosporulation occurs in some other species of Bacillariaceae, such as N.fonticola, N. angustata and apparently also N. subcurvata. Certain features are also shared by N. longissima, which shares a similar cell shape, with long rostrate apices. Two of the four plastids present in the zygotes and auxospores are often contracted and apparently degenerate. Oogamy is unlikely to occur in any members of the Bacillariaceae, though some slight doubt lingers; an old report (by Pascher), of the formation of four protoplasts (gametes?) within frustules of Nitzschia cf. hantzschiana, requires reinvestigation. The nature of the caps that cover the ends of the auxospores in many pennate diatoms is discussed.