Some Observation on the Alga Fragilaria crotonensis Kitton and its Parasitism by Two Chytridiaceous Fungi

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Abstract
It has been shown by experimentation that two morphologically distinct clones of Fragilaria crotonensis Kitton, isolated from the plankton of Windermere at approximately the same time, were affected quite differently by the chytrid Rhizophydium fragilariae Canter. In one case the diatom filaments became heavily parasitized and could be used for the maintenance of the fungus. In the other case infection was negligible. Additional clones, representative of these two morphological forms, from other bodies of water in the Windermere drainage basin were tested. The same pattern of infection or relative non-infection again ensued in direct accordance with the particular type of filament used. Some preliminary experiments undertaken with a second, as yet little known chytrid parasite of F. crotonensis are reported. In this instance the fungus appeared to find its natural host on cells belonging to the morphological form which failed to support the continued increase of R. fragilariae. The parasitism of morphological variants of F. crotonensis by these fungi in the wild from Britain and else where is discussed.