Table I. Maximum values of surface potential () reported for plant materials.

Material	mV	Reference
Sugar beet pectina	48, 60	Kuljanin et al. (2008); Nakauma et al. (2008)
Kraft lignina	45	Dong et al. (1996)
Citrus pectina	33	Kim et al. (2005)
Cellulose fibersa	15	Bellmann et al. (2005)
Xylem	14	Stamm (1926)

^aValues shown are for materials processed in acidic or basic solutions at elevated temperatures; these processes likely increase over its value in vivo. We did not find experimental data on for these materials in unprocessed conditions. In this study, we take the materials sugar beet pectin and xylem to represent the upper and lower bounds on the magnitude of the surface potential in vivo.