The fungal component in the root, and soil, and the colonised root itself. Two types of AM are common, Arum and Paris, though some plants form intermediate types, indicating that the host determines the structure of the intraradical component. In general terms, the Arum type of AM consist of a hyphal network which extends through the intercellular space of the root cortex. Arbuscules form from lateral projections which invaginate cortical cells. The arbuscule collapses after a 4 to 20 days and the only evidence of its former presence is a slight unevenness of the intercellular hyphae.
Vesicles tend to be intercellular, and usually located in the cortex.
Fig W Paris type of AM are highly variable. They usually have extensive development of intracellular hyphae in the cortex, surrounded by host plasmalemma. Coils are common in a range of hosts, though these may be peletons familiar to orchid associations, or more hand-like structures which branch within the cortical cell. Arbuscules may arise as lateral projections from coils. The size and density varies enormously between host species.