“Tulip-Root” in oats caused by the stem eelworm, Anguillulina dipsaci, is of widespread occurrence in Great Britain, annually effecting much damage to oat crops which results in diminished yields of grain. At this Institute the disease has been under investigation for some years and during the seasons 1935, '36 and '37 tests have been carried out on the susceptibility to it of a number of different oat varieties. An outcome of some practical importance has resulted from this work in that it has been found that two varieties of winter oats have, for three seasons, proved resistant to attack though grown under the same conditions and subject to the same risk of invasion by the parasite as other varieties which have proved susceptible to attack. These two varieties have consistently manifested no symptoms of disease during the three seasons and on microscopic examination have been found to harbour very few examples of the parasite whereas susceptible varieties have shown the characteristic symptoms of disease in stunted growth, greatly swollen discoloured leafbases and their tissues have harboured large numbers of the parasite. The purpose of the present paper is to put these facts on record and to give some account of the investigations out of which they have arisen.