In a recent paper the writer (Goodey, 1943) has shown that the stem eelworm, Anguilulina dipsaci, occurred in considerable numbers in the scape, i.e. the flower stem, and the inflorescence of onions grown for seed in Sussex during 1943. The worms, mainly consisting of infective larvae, occurred in the dry papery tissues lining the hollow scape, in the pedicels of the flowers and in various of the floral organs, such as withered sepals and petals, in the receptacle and placenta and on the walls of the seed capsule. They were also attached to the outside of the ripened seed. In a second paper (Goodey, 1945) it is further shown that the parasite becomes firmly attached to the seed chiefly in the region of the hilum, whence it cannot be removed by the usual processes of winnowing and cleaning. The foregoing results were obtained from plant material in a dry condition and seed samples which had been threshed and cleaned. Study of this material had made it evident that the parasite must somehow gain access to the living tissues of the scape and inflorescence as these grow from the parent bulb, but it was not apparent how this came about; whether from lightly infected parent bulbs or direct from the soil. Circumstantial evidence had been adduced in the two papers, already mentioned, pointing to lightly infected parent bulbs being the probable source of infection, but the whole matter needed further investigation to elucidate this and other points. In the present communication the results of studies directed to the solution of these questions are given.