For about twenty‐five years a fairly widespread disease of bulbous iris has been known, the cause of which has always been attributed to a biologic race of the stem eelwormDitylenchus dipsaci(Kühn, 1857), Filipjev, 1936.Thorne (1945) showed that the nematode causing rot in potato tubers is different fromD. dipsaciand named itD. destructor.This nematode has since been reported fromMentha arvensisL. by Hurst (1948) and fromSonchus arvensisL. by Goodey&Goodey (1949).Examination of nematodes from diseased iris bulbs showed them to possess rounded tail tips and six incisures on each lateral field; characters by whichDitylenchus destructoris distinguished fromD. dipsaci.Cross‐inoculation experiments showed that the eelworm causing disease in potato tubers would invade and set up characteristic symptoms in iris bulbs and, in the opposite direction, the eelworm responsible for disease in iris bulbs would give rise to characteristic symptoms in potato tubers. Transfer was also effected from potato and iris toMentha arvensisand from iris toSonchus arvensis.The history of the disease in bulbous iris is briefly reviewed and the biology ofDitylenchus destructordiscussed and compared with that ofD. dipsaci.The conclusion thatD. destructoris the nematode causing eelworm disease of bulbous iris has been reported earlier (Goodey, J. B. 1