Fig. 2

Lignin distribution in poplar tracheid cell wall imaged by stimulated Raman scattering microscopy by lignin’s aryl ring stretch at 1600 cm⁻¹ (reprinted from [11] with permission). Lignin is unevenly distributed in cell wall layers. Highest lignin content is shown in the cell corner (CC), compound middle lamella (CML), and the warty layer (WL). Secondary wall (SW) has a lignin distribution gradient from outside (high) to inner side (low). Scale bar = 5 μm