Summary: A microaerophilic plectridium identified as Clostridium pectinovorum , and Cl. butyricum , were the major sporulating organisms found on English flax. Both these organisms were non‐pectolytic and unable to ret flax. An orange pigmented anaerobe, identified as Cl. aurantibutyricum , was found as a minor organism, occurring on some samples only. This organism was remarkably pectolytic and an active retting agent. Bacillus polymyxa , which attacks pectin and is a moderately active retting agent in aerobic and anaerobic rets, was occasionally found. Cl. tertium , which has been reported on English flax and in flax rets, and is regarded as an active retting agent in aerated and non‐aerated rets, proved to be non‐pectolytic and showed no retting ability. It was identical with Cl. pectinovorum .