WATER CONDUCTING SYSTEM OF THE ROSE SHOOT

Vessels, which characterize vascular plants such as Rosaceae, are among the most extraordinary cell structures in plant world: a vessel indeed is the last state of a linear file of hundreds of living cells which, in 2–3 days, together increase in diameter, 10 times more than their neighbouring cells, before simultaneously dying.
That "collective suicide" serves the community of all parenchyma living cells: such a long hollow structure, so made, becomes a new conducting way for ascending sap.

In addition to this function, vascularization also is a permanent and cumulative trace of the internal plant structure.
Primitive vessels are formed with each primordium in the buds: first vessels (primary xylem) are able to grow in length with the young organs, by cell elongation; primary xylem and phloem form parallel and separated bundles along central pith.
As organs reach their definitive size, a second generation of vessels appear, cells of which are able to grow in diameter; they are formed in the wood (secondary xylem) and their number increases with time: 1000 – 1500 vessels can be counted in the wood of a median section of rose shoot.

Primary xylem conducts water to leaves by petioles and to flower by peduncle, secondary xylem acting as an axial water reservoir, permanently full and fed (fig. 1). Young sprout first is connected to the branch by primary bundles.
Later woods of shoot and branch develop together (fig. 2).

Secondary vessel length don’t reach more than 15 cm: along the stem of rose shoot up to flower, ascending sap flows in a succession of adjacent vessels each to others connected by little apertures, finally passing from secondary to primary vessels.

II International Rose Symposium

J.P. André

https://doi.org/10.17660/ActaHortic.1996.424.67