Treating IBV with S. nigra extracts compromises virion structure. Virus was treated with 8.0 x 10-3 g/ml of S. nigra extract or solvent (vehicle) alone for 10 min before being prepared for transmission electron microscopy with negative staining. A) Most frequent virion structures observed. bar = 100 nm. Arrows indicate vesicle structures. B) Aggregates of vesicle structures observed only in virus samples treated with S. nigra. bar = 100 nm.