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Figure 4.40 Nodule anatomy showing (a) a cycad (Macrozamia miquellii) nodule consisting of a central vascular strand (VB) and an infected cortical region (stars); (b) a cyanobacterium, a microsymbiont, is located in the intercellular spaces of this infected cortex; (c) a nodule of the river-oak (Casuarina cunninghamii) consisting of a central vascular bundle with infected cells in the cortex (arrows) identified by subersation and lignification of their walls (section stained with berberine sulphate and viewed under epi-fluorescence optics); (d) scanning electron micrograph of an actinomycete microsymbiont (a filamentous bacterium) encapsulated within threads (arrow) throughout the plant cytoplasm; (e) a legume (Macroptilium lathyroides) nodule consisting of a central infected region with scattered infected cells (arrows) enclosed in a cortex. Vascular strands (VB) are present in the cortex; (f) transmission electron micrograph of a soybean (Glycine max L.) nodule containing a microsymbiont enveloped by plasma membrane to form ‘symbiosomes’ — packets of bacteria within the cell cytoplasm (arrows). Scale bar = 100 µm in (a), (b), (c) and (e); 5 µm in (d) and (f). (Images courtesy K. Walsh)