SUMMARYGoodyera repens Br. was either grown from seed and infected with its natural mycorrhizal endophyte, Ceratobasidium cornigerum (Bourd.) Rogers, or obtained as natural mycorrhizal plants from the field. Insoluble [^*C]carbohydrate was provided at a point source available only to the external mycorrhizal mycelium of protocorms, plantlets (up to 50 mg w wt) or plants. Protocorms and plantlets obtained ^*C via their external mycelium but plants did not, even when stressed for carbon by being kept in darkness for two weeks. There was no enhancement of growth of mycorrhizal plants when a carbon source was present in the substrate over an eight-week period. When ^^COg was fed to plant shoots to monitor movement of carbon from plant to endophyte, there was no evidence of such movement over a 7 d period.These results suggest that carbon moves only from fungus to orchid and that this movement ceases when the host reaches a certain stage of development. With respect to carbon, mature green plants of G. repens appear to be independent of their mycorrhizal association.

Summary The rate of P uptake per unit length of root of adult plants of the orchid Goodyera repens Br., infected with the mycorrhizal endophyte Rhizoctonia goodyerae‐repentis Constantin and Dufour, was up to 100 times greater than that of non‐mycorrhizal plants. When the active extramatrical mycelium was reduced by treatment with thiabendazole fungicide, the relative growth rate of mycorrhizal plants was reduced in low P conditions but not in P rich conditions. Rates of P uptake into fungicide‐treated plants were Jess than those of mycorrhizal plants at both P levels. Translocation of 32P from a point source to the plant via the extramatrical mycelium was demonstrated and could be inhibited by the application of thiabendazole. In a model system incorporating a perlite/Vermiculite substrate, translocation of 32P via the endophyte took place over distances up to 9 cm. The mycorrhiza of adult G. repens appears similar to other mycorrhizas in its ability to enhance growth and P uptake.

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Summary Studies of the orchid Goodyera repens Br. growing on agar media in association with its natural endophyte Rkizoctonia goodyerae‐repentis Constantin and Dufour showed that mycorrhizal plants of different developmental stages had significantly higher growth rates and level of P and N than did uninfected ones. Treatment of mycorrhizal plants with the fungicide thiabendazole stopped growth of external mycelium and caused a significant decrease in growth rate, P and N content, percentage infection and net assimilation rate. These results suggest that the mycorrhizal fungus enhances nutrient uptake and allows greater growth rates, a situation similar to that found in non‐orchid mycorrhizas.