Ergosterol is to fungi what cholesterol is to humans: the major membrane sterol. The content of ergosterol in the living bodies of fungi is rather constant, near 5 µg per mg dry mass (with some exceptions), and ergosterol is nearly absent in other organisms of decomposition systems. Thus ergosterol can be used as a biochemical index for living mass of fungi. Ergosterol is easily measured by liquid chromatography, and detected by its uniquely strong absorbance of ultraviolet light in the vicinity of 282 nm. In this graph the chromatogram to the left is for blades of smooth cordgrass ( Spartina alterniflora) at the yellow-green senescent stage. The chromatogram to the right is for naturally-decaying blades of cordgrass about two weeks after senescence. The word "ergosterol" is shown just above the 282-nm absorbance peak in each chromatogram. The size of the ergosterol peak on the right shows the rapidity with which ascomycetes begin the pervasion and decay of cordgrass shoots in the marsh. See Gessner & Newell, 2002, pp 390-408 in C Hurst et al. (eds) Manual of environmental microbiology. Second edition. ASM Press, Washington, DC; Newell, 2001, Fungal biomass and productivity, pp 357-372 in J.H. Paul (ed.), Methods in Microbiology 30. Marine Microbiology, Academic Press, New York.