Here is what you see if you stripe the bark off a limb: dense and long wood ridges (striae) are formed on the wood underneath
the bark. It is not that wood ridges form bark bumps, but rather the ridges on the wood correspond to depressions on the bark
surface. The smooth wavy bark is diagnostic for rusty and gray willow in New England; the related American species don't have
the striae pronounced as much.