| heal.abstract |
Laurus nobilis is an evergreen shrub or tree native to the Mediterranean region. Known since ancient times in Greece it has many medicinal and culinary uses, but is mainly used for ornamental purposes in parks and gardens as well as roadside trees. Its leaves are bifacial, hypostomatic and in the temperate zone they are initiated throughout the year whenever the conditions are favourable. During the early stages of development leaves are soft and bright green in colour becoming dark green, hard and leathery when mature. This hardening of the leaves, as is revealed with light and electron microscopy, is due to secondary development of the vascular tissues, thickening and lignification of the walls of the bundle sheath extension cells and the walls of the epidermal cells. In the latter, thickening is more prominent on the adaxial epidermis with all the walls becoming thick and lignified during maturation and to a lesser extent on the abaxial epidermis with the external periclinal walls becoming thicker than the internal. Radial (anticlinal) walls of epidermal cells have field pits apparently not traversed by plasmodesmata and together with the tubular marginal pits of the external (periclinal) wall seem to provide plasticity for water fluctuations. Stomata are sunken with the guard cells embedded in the midregion of the stomatal pore side cell wall of the subsidiary cells thus allowing the opening and closing of the stomata which otherwise would have been difficult due to the hardness of the lignified epidermal cells. These anatomical characteristics allow the plant to withstand long periods of drought and make it an ideal ornamental plant for urban and sub-urban areas in temperate climates. |
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