Indirect immunofluorescence detection of the galactan (LM5) epitope in transverse sections of fern petioles and lycophyte stems. Calcofluor White fluorescence (a, d, g, h, k, l, o, r) shows the full extent of cell walls. (a–c) Abundance of the LM5 epitope in cell walls of phloem sieve cells in the vascular bundle of Blechnum brasiliense. (d–g) Similar distribution pattern of LM5 in Asplenium compressum. A high magnification (g) of a vascular bundle shows that LM5-binding is restricted to cell walls of phloem sieve cells (sc). (h–k) Binding of LM5 to the innermost cell wall layers of collenchymatous tissue in Asplenium rutifolium. (l–q) LM5 binding to most tissues in Equisetum arvense, including the cell walls of the vascular bundle and surrounding parenchyma (l–n) as well as to the inner cell wall layer of the collenchymatous strengthening tissue (o–q). (r–t) LM5 binding to phloem in the lycophyte Selaginella grandis. Abbreviations: phl, phloem; sc, sieve cell; coll, collenchymatous tissue. No primary antibody controls are provided (c, f, j, n, q, t). Scale bars: 40 μm.