Revisiting a more than century-old study on the mycorrhiza of Gastrodia elata: Rediscovery and scientific significance of slide preparations.

Microscope slide preparations made for the observation of the mycorrhiza of the mycoheterotrophic orchid Gastrodia elata were rediscovered and confirmed to be the original materials used by Shunsuke Kusano for his 1911 publication. In this study, we re-examined these historical slides to assess their preservation and scientific significance. Among the 115 slides, 61 clearly displayed the mycorrhiza of G. elata. Intracellular organelles closely resembling the 'vesicle', 'globule', 'tubular sheath', 'globular bodies', and 'lignified papillae' described by Kusano were observed, and staining reactions consistent with Heidenhain's iron haematoxylin and Flemming's triple stain remained visible in many specimens despite being more than a century old. Slides also contained tubers of Solanum tuberosum infected with mycelial strands of Armillaria mellea sensu lato, reflecting Kusano's comparative approach to symbiosis and pathogenicity.