Page "Xylem" Paragraph 43

Cavitation is hard to avoid, but once it has occurred plants have a range of mechanisms to contain the damage.

Small pits link adjacent conduits to allow fluid to flow between them, but not air – although ironically these pits, which prevent the spread of embolisms, are also a major cause of them.

These pitted surfaces further reduce the flow of water through the xylem by as much as 30 %.

Conifers, by the Jurassic, developed an ingenious improvement, using valve-like structures to isolate cavitated elements.

These torus-margo structures have a blob floating in the middle of a donut ; when one side depressurises the blob is sucked into the torus and blocks further flow.

Other plants simply accept cavitation ; for instance, oaks grow a ring of wide vessels at the start of each spring, none of which survive the winter frosts.

Maples use root pressure each spring to force sap upwards from the roots, squeezing out any air bubbles.