Question: An experimenter wished to find out if two different preparations of a virus would produce different effects on tobacco plants. Half a leaf of a tobacco plant was rubbed with a cotton swab soaked in one preparation of the virus extract and the second half of the leaf was rubbed with the second extract. The measurement of virus potency was the number of lesions appearing on the half-leaf (these lesions appear as small dark rings that are easily counted). Are the two virus extracts the same in potency?