PLATE XXI 
Red clover, showing effect of sulphates on growth of roots. A , Check; B, nitrogen, 
phosphorus, potassium; C, nitrogen, phosphorus, potassium, plus sulphur as sodium 
sulphate; D, nitrogen, phosphorus, potassium, plus sulphur as calcium sulphate; E, 
sodium sulphate only; F, calcium sulphate only. 
