The structure and function of the vegetative mycelium of ectomycorrhizal plants III. Ultrastructural and autoradiographic analysis of inter‐plant carbon distribution through intact mycelial systems

SUMMARY Plants of Pinus sylvestris L. were grown in mycorrhizal association with Suillus bovinus (Fr.) O. Kuntze in observation chambers until an interconnecting mycelial network had developed between the seedlings. The shoot of an individual seedling was then scaled in a perspex cuvette and exposed to 14 CO 2 . After incubation for 48 h, the‘donor’shoot was removed and components of the mycelial network and mycorrhizal roots of connected and unconnected‘receiver’seedlings were harvested, fixed, embedded and sectioned prior to being autoradiographed and examined by transmission electron microscopy. The patterns of distribution of 14 C‐labelled material within the mycelial strands, the sheath and root tissues was examined. The results are discussed in relation to carbon metabolism of the fungus and of the interconnected host plant.