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Oncidium heteranthum var. album: fertile flower, SEM. (A) Part of callus showing projections with overlying glabrous epidermis. Between these projections occur unicellular trichomes and papillae. (B) Residues of secreted material (arrows) occur on the surface of the papillae. (C) Secreted material (arrows) is also present on the surface of trichome cell walls. (D) Striate cuticle of callus trichomes with small blisters (arrows). Scale bars = 500 μm, 50 μm, 50 μm, 20 μm, respectively.
