Paths and Mechanisms of Moisture Movements in Detached Leaves of White Clover(Trifolium repens L.): I. Losses of Petiole Moisture direct from Petioles and via Laminae

The experiments described were concerned with losses of moisturefrom laminae and petioles of leaves of white clover (Trifoliumrepens L.) detached from parent plants, and with the resistancesin the two pathways of loss of petiole moisture-via laminaeand direct from petiole surfaces. Methods involving determination of moisture losses from separatedlaminae and petioles were unsatisfactory and transpiration chamberswere therefore used to permit determinations with intact leaves. Up to 24 per cent of the total petiole moisture was lost viathe laminae, the amount frequently exceeding that initiallyresiding in the xylem of the petioles. Stomatal, cuticular, and external resistances were calculatedat several stages of wilting. Rates of loss of petiole moistureby both pathways were controlled by stomatal and external resistancesin the early stages and by cuticular and internal resistancesin the later stages. Under certain conditions, transpirationof petiole moisture via the lamina ceased earlier than mighthave been expected; estimates were made of the resistances involved.