Water uptake from foliar-applied drops and its further distribution in the oat leaf

A fraction (12%) of the water from tritium-labelled foliar-applied drops rapidly penetrates through the cuticle and, after transport through the mesophyll, is distributed in an acropetal direction and probably through the xylem, over the oat leaf. The initial rapid penetration is favourably affected by a water “continuum” that is always formed between tissue and drop, immediately after drop application. It is suggested that the pathways for the creation of this water continuum are the ectodesmata in the guard cells of the stomata. Increasing the calciumchloride concentration of the applied drops has little influence on the water uptake from these drops. Higher salt content of particular parts of the oat leaf increases the water retention by these parts. In the present experimental conditions (60-70% relative humidity) aqueous vapour uptake from the ambient air is small (1,7% of the amounts evaporated), as compared to the uptake from applied drops. Tritium from foliar-absorbed water does not combine with stable compounds (mainly organic) in the leaf.