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The most detailed observations of the development and structure of monotropoid mycorrhizas have been obtained from studies on the genus Monotropa. In M. uniflora and M. hypopitys, clusters of roots form, each root becoming ensheathed with fungal hyphae, resulting in a well-developed mantle. Details of the mantle can best be seen using scanning electron microscopy. Frequently, large calcium oxalate crystals are deposited among the outer mantle hyphae and along the surface of hyphae within the mantle. Cystidia may be present, depending on the fungal species. Rhizomorphs are usually present and have been traced in vivo from the surface of M. hypopitys mycorrhizas to the roots of neighbouring pine trees.
Roots of Pterospora andromedea also occur in coralloid clusters, with each root forming several laterals. The mantle covers the main root and lateral roots. Hyphae of the external mantle are very irregular in shape, and small crystals are present on their surface.
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