Color-enhanced Scanning Electron Micrograph (SEM) of mullein (Verbascum thapsus) pith. The pith in the stems of dry plants such as this has the microstructure of a solid foam of air cells, ranging in size from approximately 100 to 150 micrometers in diameter. Image width: 2464.9 micrometers. Magnification: 40.5x if the image is printed 10 cm wide.