According to imbibition theory
I. ascent of sap could takes place by imbibition through the walls of xylem.
II. Water can rise through the wall due to imbibitional pressure upto a certain height only.
III. The pressure at the transpiring surface falls below that of atmsophere.
IV. rate of transpiration is roughly equal to the rate of imbibition.
A. I and II
B. II and IV
C. Only IV
D. Only III