Page 85 - PG 101-Course notes مذكرة النظري 24-25 with spec

Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

3-Vascular cylinder (Stele)

● It is surrounded by the pericycle. The pericycle consists of one layer of thin-walled

parenchyma cells, rarely more than one layer.

● The vascular tissues are phloem and xylem on alternating radii.

● Xylem: is differentiated into proto- and meta- xylem

Proto-xylem has narrow vessels and locates opposite to the pericycle, the meta-xylem

vessels are wider and directed towards the center.

❖ Some Notes:

▪ The xylem in the root is described as exarch.

▪ The xylem or phloem strands may vary from 2-8 in dicots

▪ In monocots, the strands are numerous.

▪ In dicot roots, the pith is usually very narrow or absent.

▪ In monocot roo ts the pith is always present and consists of parenchyma cells.

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