Resistance to water flow in the intracoleoptile internode of wheat

Abstract

Measurements of xylem vessel number and radii in the seminal roots and intra-coleoptile internode (I.C.I.) of five wheat genotypes showed that the conducting capacity of the I.C.I. was close to the main seminal axis, and would restrict flow when the usual 3–5 seminal axes contributed to uptake. The length and hence resistance of the I.C.I. increased with sowing depth, whilst xylem diameter also fell in two genotypes, which would further restrict flow. The resistance per unit length of I.C.I., assuming Poiseuille flow, was 4×10−4 cm−4 day MPa. A pressure drop of 0.15 MPa along an I.C.I. 5 cm long would be required to maintain transpiration under typical field conditions in southern Australia in spring.