Why are xylem cells usually dead when they conduct water?

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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.

Xylem cells are typically dead when they conduct water because their protoplast—the living material of the cell—breaks down and dissolves once their cell wall growth is complete.1

This process, a form of programmed cell death, is essential for the plant's vascular function. By clearing out the internal contents of the cell, the entire interior becomes an empty, hollow space, which allows for the rapid and unimpeded transport of water and dissolved minerals from the roots to the rest of the plant. These remaining cell walls are reinforced with lignin, providing the necessary structural strength to support the plant while serving as a conduit for long-distance transport.231