Water Pathways in Wheat Leaves. I. The Division of Fluxes Between Different Vein Types

Abstract

This study concerns the pathway of water movement through the vascular system of the wheat leaf blades. These water pathways were followed using three kinds of markers dissolved in the transpiration stream by which the patterns of water reticulation were made visible. There was a partitioning of the total water flux between the veins of the different types. The lateral veins dominate the conduction of water along the leaf from the base, and also distribute water to the mesophyll in their immediate vicinity. The intermediate veins receive water from the lateral veins in the transverse direction, via the transverse veins. The intermediate veins are primarily involved in the distribution of water to the mesophyll in their vicinity. Since there are more intermediate veins than lateral veins across the leaf blade they are the more important distributors of water to the mesophyll. The transverse veins are the pathway by which water is moved transversely from the lateral veins to the intermediate veins. Water can also be conducted in both directions, or in either direction, from its point of entry into an intermediate vein from a transverse vein. This versatility enables the network of transverse and intermediate veins to act as alternative pathways for longitudinal water conduction in the event of damage to a lateral vein.