In this and a related project funded by ARC, four fungal isolates of each of two common species were compared for their effect on plant growth. From this research we have concluded that the variation within one species is as great as the variation between species of VAM fungi. The first aim was to develop our understanding of each fungus so that we could predict the effect that fungus would have on growth of cotton. The practical consequence of our work is that knowing the species of fungus present in a soil provides us with little capacity to predict how it will influence plant growth