Noun
A wood cell with spiral or other markings and closed throughout, as in pine wood.
Source: Webster's dictionaryAn embolism is where an air bubble is created in a tracheid. Source: Internet
During the Devonian, maximum xylem diameter increased with time, with the minimum diameter remaining pretty constant. citation By the middle Devonian, the tracheid diameter of some plant lineages ( Zosterophyllophytes ) had plateaued. Source: Internet
A tracheid, once cavitated, cannot have its embolism removed and return to service (except in a few advanced angiosperms which have developed a mechanism of doing so). Source: Internet
For this reason, pits in tracheid walls have very small diameters, to prevent air entering and allowing bubbles to nucleate. Source: Internet