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How do tyloses block water movement in hardwood vessels?

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temperate softwoods and hardwoods selected to show variations — wood Temperate softwoods (left column) and hardwoods (right column), selected to highlight natural variations in colour and figure: (A) Douglas fir, (B) sugar pine, (C) redwood, (D) white oak, (E) American sycamore, and (F) black cherry. Each image shows (from left to right) transverse, radial, and tangential surfaces. Click on an individual image for an enlarged view.

Tyloses are balloonlike outgrowths that originate from parenchyma cells. These outgrowths bulge through the circular bordered pits of vessel members in hardwood, effectively blocking the movement of water through the vessels.1