In tobacco sap, the thermal inactivation point (10 min) is 75-80°C, the dilution end-point is 10-4-10-5 and the virus retains infectivity for about 30 days at room temperature. Very little infectivity is lost after 1 year in frozen sap or in desiccated leaves (McKeen, 1959). The virus is precipitated by 40% saturated ammonium sulphate and the infectivity of clarified extracts is unaffected between pH 4 and 8 (Dias & Doanne, 1968)