Multiscale imaging of M. × giganteus cell wall architecture by FM and TEM. FM images showed intact clusters of cells in raw M. × giganteus tissues (a, b) with trace evidence of mechanical damage near Pxv from the cutting process (a, asterisk). The ultrastructure of Sf including compound cell corner (Ccml), compound middle lamella (Cml), secondary wall (Sw) and cell lumen (CL) were observed by TEM (c). In samples pretreated at 160°C, 0.5% H2SO4 for 15 min, individual cell walls were shown to be separated, particularly at the St and Com regions (d, white arrows) and at the Sf–Par boundaries (e, white arrows). A TEM scan of Sf presented lighter staining in the Ccml indicating lower density in these regions (f, white triangle). Samples pretreated at 170°C, 1% H2SO4 for 30 min exhibited many crushes of broken cells (g). Increased disjoining of Par walls from the Cml can be clearly distinguished at higher magnifications (h, white arrows). Additionally, intercellular spaces at the Ccml of Sf were gradually generated, resulting from the removal of hemicelluloses and lignin (i, white triangle). Sf sclerenchyma fibers, Par parenchyma, Pxv protoxylem vessel, Mxv metaxylem vessel, St sieve tube, Com companion cell.