Parenchyma is not the sole site of storage: storage in living fibres

Storage of nutrients and water are important functions of secondary xylem that have received much attention lately. In most of these studies, the storage role has been attributed to the fraction and arrangement of ray and axial parenchyma. However, in the current article, we show that in many species, especially those from tropical and subtropical regions (where most of the world's plant species are found), nutrient and water storage is carried out by living imperforate tracheary elements (ITEs), colloquially termed "living fibres". The occurrence of living fibres has been long recognized by anatomists, and especially emphasized in the work of Sherwin Carlquist. In spite of this, living fibres have remained largely unacknowledged by most plant physiologists and ecologists. To raise awareness about the existence of living fibres and to celebrate the illuminating work of Sherwin Carlquist, we summarize our current understanding of the structure, function, and occurrence of living fibres and emphasize that they should receive more attention when studying storage in wood.