Abstract
The distribution of microorganisms on and around roots, and their effects on higher plants, are discussed. Bacterial effects on plant nutrition are uncertain, and direct effects seem likely to be small. Mycorrhizal fungi can improve plant nutrition greatly, usually by increasing phosphate supply, and the mechanisms are now fairly well understood. The distribution of microorganisms on and around roots, and their effects on higher plants, are discussed. Bacterial effects on plant nutrition are uncertain, and direct effects seem likely to be small. Mycorrhizal fungi can improve plant nutrition greatly, usually by increasing phosphate supply, and the mechanisms are now fairly well understood. © Williams & Wilkins 1975. All Rights Reserved.