Ectodesmata in relation to binding sites for inorganic ions and urea on isolated cuticular membrane surfaces

Binding of radioactive ions and molecules penetrating isolated cuticles of green onion leaves does not occur in the whole cuticular membrane but is restricted to pointlike areas of a characteristic distribution as was recently demonstrated by microradioautography. Comparison of the localization of these binding sites in isolated cuticles and of ectodesmata in outer epidermal walls reveals that the pattern of binding sites coincides with that of ectodesmata. It is concluded that in intact epidermal cells the binding sites in the cuticle lie on top of ectodesmatal spaces in the wall and that together they form combined pathways of favored penetrability for aqueous solutions which are to be absorbed or excreted.