What good are knees to a baldcypress?

What good are knees on a tree? Baldcypress famously has these odd structures that stick out above the water line. Botanist Francois André Michaux saw knees on baldcypress trees and, in 1819, said “No cause can be assigned for their existence.”  Nearly 200 years later, what do we know about the function of this strange structure? […]