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Abstract
The tube-dwelling marine diatom Navkula pseudocomoides Hendey was kept in culture for over two years. In contrast with tubes formed under natural conditions, those formed in culture are single, lacking the secondary tube structure so typical of this species.
It is proposed that tube formation is a two-phase process. Newly formed parts at the end of the tube are very thin, flexible and have a net-like wall structure. Subsequently the wall is thickened by the addition of new material secreted by the diatoms, maybe during their very slow and rhythmic to and fro movement inside the tube.
After some time in culture it became apparent that the various newly formed tubes were filled with cells of very different lengths, although the culture was started with a single strand of secondary tube collected in nature. From this and additional observations on natural material, it was concluded that a secondary tube of Navicula pseudocomoides, made up of a bundle of primary tubes, is not exclusively filled with clonal cells, contrary to the findings of previous investigators. The primary tubes, however, are exclusively filled with cells of nearly the same length, and are clonal.
