1. The resistance of the hop-mildew (Sphaerotheca Humuli (DC.) Burr.) to polysulphide solutions varies according to its stage of development. The earliest stages after infection and antecedent to the production of conidiophores are the most resistant, requiring approximately a solution of double the concentration lethal for the “powdery” conidial stage. The “powdery” conidial stage occurring on young leaves is more resistant than the same stage on older leaves.
2. Conclusive proof has been obtained that with polysulphide solutions neither the total sulphur content nor the sulphide sulphur content gives an index of their fungicidal value.
3. The percentage of polysulphide sulphur in polysulphide solutions appears to be the factor determining their fungicidal value.
4. The fungicidal value of such solutions does not depend upon the nature of the polysulphides present.