Comparative effects of cobalt, nickel and copper on plant growth

SUMMARY 1. An account is given of the present position of our knowledge with regard to the distribution and the physiological importance of nickel and cobalt, in relation to plants and animals. 2. Experiments on barley and broad beans were carried out in water cultures with the sulphates and chlorides of cobalt, nickel and copper. 3. In every case a range of low concentrations did little or no damage, but toxic action occurred abruptly above a concentration which varied with the species and with the compound. 4. With barley, copper was the most poisonous element in either compound, but the differences were not striking. Low concentrations of the sulphate were innocuous, but parallel low strengths of the chloride caused a slight, significant depression in growth. 5. With broad beans, cobalt was much more poisonous than either nickel or copper, particularly with the sulphate. No slight depression with low concentrations of the chloride was noticeable with this species. 6. The morphological response to toxicity varied with the element concerned. Copper, in poisonous strengths, caused shortening and ?bunching? of barley roots, whereas nickel and cobalt permitted the growth of elongated roots of a very attenuated nature. 7. The individuality of plant response to poison was frequently shown by the great variation in growth in the borderline concentrations just below those which caused marked depression of growth.