Anabaena azollae can be completely eliminated from megasporocarps of Azolla by the removal of the indusium and apical membrane after horizontally cutting the megaspore apparatus beneath the apical membrane. All subsequent sporelings of Azolla are free from Anabaena. These do not fix N and fail to survive on N2-free media. They grow normally, however, in N2-containing liquid medium or in a soil-water system with small amounts of added N and eventually bear sporocarps. Anabaena is again absent in the new megasporocarps and sporelings of Azolla derived from the second generation of megaspores are likewise Anabaena-free.
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