Root Pressure in Conifers.
Exudation of sap was never observed to occur from stumps of detopped seedlings of loblolly pine or white spruce, but measurable exudation occurred from apical root segments, 4 to 8 centimeters long, which were removed from the root systems and observed individually. Fully suberized root segments of loblolly pine exuded as much or more sap than unsuberized roots. Exudation also occurred from detached sugar maple root segments, but not from stumps attached to entire root systems.
O'leary
J W
JW
Kramer
P J
PJ