Elements that are required by plants in large amounts are called macronutrients. Elements like carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium are macronutrients. The concentration of essential elements below which plant growth is retarded is termed as critical concentration. The deficiency of different elements causes different symptoms in a plant. Elements like carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium are macronutrients. The concentration of the essential element below which plant growth is retarded is termed as critical concentration. Carbon, hydrogen and oxygen are derived by plants from water and by gaseous exchange. Plants obtain nitrogen from the soil either in the form of nitrate, nitrite or ammonium salts. The deficiency symptoms of nitrogen are chlorosis, and inhibition of cell division. Phosphorus is absorbed by the plants from soil in the form of phosphate ions. Deficiency of phosphorus shows symptoms like loss of older leaves, poor growth, dull green colouration of older leaves and yellow colouration of lower leaves. Potassium sulphate and potassium nitrate supplies the plant with potassium. Deficiency of potassium leads to chlorosis, necrosis, rosette or bushy habit of growth, reduction in stem growth and inhibition of cell division. Plants obtain sulphur from the soil. Sulphur deficiency leads to symptoms like chlorosis, and inhibition of cell division. Calcium is absorbed by plants in the form of calcium ions from calcium carbonate. Deficiency of calcium leads to death of meristematic tissues, stunted growth and necrosis. Magnesium is available as exchangeable cation in the soil. Deficiency of magnesium leads to chlorosis, and necrosis. This leads to the withering of leaves.