Morphological Features of Synthesized Ectomycorrhizae of Alnus Crisp a and A. Rugosa*

SUMMARY The ability of two shrubby alders to form ectomycorrhizae with known species of fungus was investigated. Frankia‐ inoculated seedlings of Alnus crispa and Alnus rugosa were raised in growth pouches and inoculated with a pure culture inoculum of potential ectomycorrhizal fungi. Ten of the 46 species of fungi used formed ectomycorrhizae with both Alnus species. Only Alpova diplophloeus showed a well distributed Hartig net; others had a net only proximally, while others had none. These patterns are discussed in terms of more or less rapid Hartig net development. The Hartig net was always confined to the epidermal layer of the root, never completely surrounding it. This situation appears to predominate in the Angiosperms. Colonization of young actinorhizae by Alpova diplophloeus led to the formation of ectomycorrhizal structures.