Indirect immunofluorescence detection of the mixed-linkage glucan epitope (BioSupplies 400–3) in transverse sections of fern petioles and lycophyte stems. Calcofluor White fluorescence (a, d, g, k, o, s, v, w) and bright-field (m) showing the full extent of cell walls. (a–n) Localisation of the MLG epitope in Asplenium elliottii. The epitope is detected in collenchymatous (d–f) and sclerenchymatous (g–j) mechanical tissues as well as in epidermal cell walls. Parenchyma shows differential labelling intensities with stronger labelling of parenchyma walls surrounding mechanical tissues. Increased labelling is observed in parenchyma tissues bordering the hypodermal sclerenchyma (g–j) and the zone with sclereids surrounding the vascular bundle (k–n). Weak labelling is observed in the phloem tissue. (o–r) The anti-MLG antibody binds to parenchymatous cell walls in Blechnum brasiliense. Cell walls of the sclerenchyma sheath (ss) and subepidermal sclerenchyma (scler) are not labelled. (s–w) Detection of the MLG epitope in the collenchymatous strengthening tissue (coll) of Equisetum arvense. Higher magnification (v, w) shows that the epitope is restricted to secondary cell walls. (x, y) Labelling of a continuous ring of parenchyma tissue located between the central cavity and vascular bundles. Abbreviations: coll, collenchymatous tissue; scler, sclerenchyma; e, epidermis; scl: sclereïds; t, tracheids; ss, sclerenchyma sheath; vb: vascular bundle. No primary antibody controls are provided (f, j, n, r, u, y). Scale bars: a–c, 1 mm; d–w, 40 μm.