Nitzschia Cultures at Hull and at Plymouth

Abstract

MORE than thirty years ago a persistent culture of a minute diatom was obtained by Allen and Nelson¹; they refer to it as Nitzschia closterium, W. Sm., forma minutissima. This persistent culture has been maintained at Plymouth ever since, and has been distributed to many workers at home and abroad. The species has proved to be a useful food for many kinds of marine larvae and a convenient diatom for experimental work. A sample was sent to Hull about 1930 and has been grown there until the present time. When first sent the great majority of the frustules, as at Plymouth, were of the straight or slightly curved fusiform shape characteristic of the species, but in 1932 a very few three-rayed or tri-radiate cells were present; their abundance was certainly much less than 1 per cent. In cultures derived from Plymouth stock such cells have been seen by other workers, notably by Barker². By 1934 there had, at Hull, been a slight increase in the abundance of these tri-radiates and they may have formed as much as 1 per cent of the cultures. In 1936 the proportion had risen to more than 50 per cent. Thereafter the abundance of tri-radiates steadily increased so that by the spring of 1939 they comprised 97 per cent, and by the summer of 1941 more than 99 per cent, of the cultures.