IN most plants nitrate is the form in which nitrogen is absorbed from the soil and translocated upwards from the roots. Accumulation of nitrate in upper parts of the plant may follow, nitrate reduction and formation of organic nitrogen compounds occurring in many organs. Thomas1 showed that the nitrogen uptake of apple trees was atypical in that nitrates could normally be detected in only the finest roots, and suggested that nitrate reduction and formation of amino-acids occurred in these organs. Absence of nitrates from apple leaves has since been confirmed by many workers; but under certain conditions they have been detected2.