arbuscular mycorrhiza: (abbr. AM; syn. endomycorrhiza)  
symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants in which fungal hyphae invade cortical cells of the root and produce vesicles and arbuscles (see ectomycorrhiza)
(endomycorrhizal vesicles in alfalfa root stained with trypan blue)

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