Seedlings of Eucalyptus dumosa A. Cunn. ex Schau., derived from a parent tree growing in a patch of calcareous soil, grew very poorly or not at all in that same soil unless they had formed abundant mycorrhizas. Other seedlings of that tree, planted in non-calcareous soil from the same locality, grew well with negligible mycorrhizas. Similar results were obtained using synthetic calcareous and non-calcareous potting mixtures. E. dumosa appears therefore to be primarily a calcifuge species, which becomes secondarily or facultatively calcicole as a consequence of mycorrhiza formation. Inflow of calcium into the seedlings with many mycorrhizas was the same as that into seedlings with few, but phosphorus inflow was greater into the mycorrhizal system. Mycorrhizas were presumably more effective at mobilizing and accumulating phosphate from insoluble calcium phosphates in the calcareous substrates than were uninfected roots.
Early infection of the seedlings was almost entirely by VA endomycorrhizal fungi, in contrast to the ectomycorrhizal fungi which are usual in eucalypts. Most of the growth stimulus seemed to be associated with these early endomycorrhizas. Ectomycorrhizas formed later and tended to replace the endomycorrhizas. The ectomycorrhizas which succeeded the endomycorrhizas in inoculated pots were of a different type (hyaline) from those (black) which developed spontaneously, presumably from airborne spores, on uninfected roots in uninoculated pots.