Amongst biological strains or races of the.stem eelworm, Anguillulina dipsaci, some are comparatively polyphagous and are capable of causing disease in a number of different host plants whilst others are restricted to one or two hosts. The strain causing “ tulip root” in oats is usually regarded as a restricted one being Confined to oats or, as in Yorkshire, to oats and beans, in which infection takes place in the seedling stage and persists during the greater part of the life of the plant. Whether the parasite will attack other agricultural plants is a matter of some practical importance and since in a crop rotation a seeds mixture for ley production may follow oats, it was decided to test whether the parasite would infect plants comprising a typical seeds mixture. It was also hoped to determine whether any of the grasses or clovers would be more or less permanently affected and thus serve as reservoir hosts for the parasite and so enable it to tide over the period between successive oat crops. The present paper deals with pot experiments set up to test this matter as a result of which it has been found that the oat strain of the parasite is capable of causing serious injury to the young seedlings of a number of grasses and clovers of a seeds mixture.