| Abstract: | Water in the transpiration stream is distributed throughoutthe leaves in the vascular bundles. In wheat, water appearsto be confined to the main veins by the mestome sheath and toenter the mesophyll through the walls of the smaller veins.Within the mesophyll the water in the transpiration stream movesin the free space of the cell walls to the evaporating surfacesof the leaf. The lead chelate, which is used to trace the transpirationstream, accumulates at the final points of evaporation at themargin of the leaf. Lead chelate accumulates beneath and onthe surface of the cuticle, being partly associated with theanticlinal walls of the epidermal cells, the walls of the stomatalguard cells and specialized epidermal cells. Chelate does notaccumulate at the base of substomatal cavities, indicating thatthe cuticle of the epidermis is the main evaporating surfaceof the leaf. The behaviour in broad bean, laurel, and plantainis essentially the same. The rate of peristomatal and cuticulartranspiration is closely related to the size of the stomatalaperture. Conditions which control stomatal aperture also causechanges in the dimensions of the epidermal cells. |
