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The paper-sandwich technique for simultaneous inoculation of populations of root apices, was used to produce numbers of synchronously developing ectomycorrhizas, and to permit direct time-sequencing of stages in the infection process in eucalypts. After one day there was evidence of chemical interaction between fungus and host. By two days, sheath formation had started in the cap region, cap cells were invaded by fungus, and apical root tissues commenced to swell. By four days all the anatomical features of an ectomycorrhiza were present, including the Hartig net. Thereafter, mycorrhizal features were merely enhanced and perpetuated by subsequent acrogenous development of the fungus-root dual organ. The process of mycorrhizal perpetuation involved the same sequence of events (sheath development at the apex associated with invasion of cap cells, modification of other root tissues, then finally formation of Hartig net) as did the initial infection process. [ABSTRACT FROM AUTHOR]