Relationship between diameter of the filament and cell shape in blue-green algae

Observations on infralittoral blue-green algae and a literature survey show that filamentous blue-green algae of average size tend to have isodiametric cells, while the very narrow ones often have cylindrical cells and the very large forms have only discoid cells. A possible interpretation of this phenomenon is presented, based on the short life of prokaryotic messenger RNAs.