Sieve tube element
From Freepedia
The names Sieve tube element and Sieve tube member are synonyms and are used to describe a certain type of elongated cell in phloem tissue. At the ends those cells are connected with other sieve elements, and together they constitute the sieve tube. The main function of the sieve tube is transport of carbohydrates in the plant (e.g., from the leaves to the fruits and roots).
The forest botanist T. Hartig was the first to discover and name these cells as Siebfasern (sieve fibres) and Siebröhren (sieve tubes) in 1837.
Unlike vessel elements, which are elongated cells that transport water and minerals in the xylem/wood, and represent another kind of vascular tissue in the plant, sieve elements are living cells. However, they do not have a nucleus (it degenerates during differentiation).
Sieve tubes from a Meliaceae species (s), Parenchyma cells (p)
References
Katherine Esau (1969). The Phloem -in: Encyclopedia of Plant Anatomy. Gebrüder Borntraeger, Berlin, Stuttgart.
