Page 201 - PG 101-Course notes مذكرة النظري 24-25 with spec

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

= annual growth layers (tree rings).

- Wood = tracheids, vessel elements and fibers.

b. Cork cambium --> - During secondary growth, epidermis from
cork primary growth splits, dries and falls off stem

- Cells in outer cortex (outside secondary
phloem) become meristematic and divide to

form cork cells on outer perimeter; cork cells

deposit waxy material (= suberin) in their cell

walls, then die. Cork are dead cells.

- Periderm = cork cambium + cork; replaces

epidermis, provides protection against pathogens,

waxy walls retard water loss (bark includes

periderm and phloem)

C. Plant Hormones

- As in animals, plant hormones = chemicals for communication

- Hormone = a chemical released from one cell that affects growth, development

of target cells which have appropriate receptors.

- Unlike animal, hormones that act on distant cells, plant hormones can act on

adjacent cells as well as distant ones- There are five known categories of plant

hormones.

1. Auxins - Produced by shoot apical meristem tissue.

- Promotes cell elongation in stems, coleoptiles (= protective
sheath covering monocot shoot during germination.

- Promotes development of lateral roots, even at very low
concentrations; may also participate in stem, root growth

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