The Petiole

The petiole is grooved on the upper surface. The epidermis is made of hexagonal cells, the cuticle is thick and corrugated in appearance. Below the epidermis there is a band of collenchyma, followed by 10-12 rows of parenchymatous cells. The central position is occupied by a mucilage cavity. The vascular bundles are distributed in semi circular fashion. They are open, collateral and enclosed in a parenchymatous bundle sheath. The bundles just below the groove are very small (usually three in number) and each of them consists of 4-5 xylem elements only. On the two corners adjacent to the middle groove, there are two bundles larger than the others. Here the protoxylem elements are oriented towards the central mucilage cavity (endarch). The bundle opposite the groove is the largest, which along with the two adjacent bundles is located slightly towards the interior compared to the rest of the bundles. The xylem consists of vessels and tracheids, phloem of sieve tubes, companion cells and phloem parenchyma. Cambial zone consists of 2-3 layers of narrow elongated cells. Pearl glands are seen on the petioles. In the vegetative node the petioles are sheathed, which are extension of petiole towards the sides and these sheaths are caducous (Fig. 2.6)

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