SUMMARYSeedlings of leek were grown in a factorial experiment to examine the interactions between mycorrhizal infection with Glomus fasciculatus, soil teachings and the Collembola, Folsomia Candida. The growth of leek was increased by mycorrhizal infection and leachings, the latter having a lesser effect, and reduced by F. Candida. There was a strong interaction between the effects of mycorrhizal infection and the presence of F. Candida since infected plants in pots with the Collembola grew little better than uninfected plants. Evidence from root weight ratios, phosphate inflows and the gut contents of the Collembola all suggest that this is due to grazing of the external hyphae of G. fasciculatus, so rendering the infection ineffective.