BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VII. PLANT TISSUES

Vascular Tissues

Vessels (Tracheae)

They originate from ordinary parenchymal Cells beneath the SHOOT apex through the dissolution of transverse Cell walls. They form a vertical row of dead cell-segments interconnected by one or more perforations located within perforation plates. The length of a vessel segment is 0.2-0.7 mm, while the vessel itself ranges from several centimeters up to 5 meters. They reach giant proportions in lianas (climbing plants).

A secondary wall is deposited on the inner surfaces of the vessel segments, resulting in characteristic annular, helical, reticulate, scalariform, and pitted thickenings. The lateral walls of vessel segments contain pits through which Water moves to adjacent cells. The perforation plate situated between vessel segments can be horizontal or oblique. Horizontal plates typically feature a single perforation, whereas oblique ones have several. Unlike tracheids, vessels are longer and wider, making them far more efficient for water conduction.

Primary tracheids and vessels differentiate from procambium, while secondary ones originate from cambium. Annular and helical conducting elements develop in young, rapidly growing plant Organs, whereas reticulate, scalariform, and pitted elements form in older organs that have ceased growing. In terms of spatial arrangement within the plant organ, annular and helical Tissues lie closer to the center, while reticulate, scalariform, and pitted tissues are located closer to the periphery.