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In this article we will discuss about the transverse sections of petiole of some flowers:- 1. Cucurbita 2. Sunflower 3. Piper Betle 4. Waterlily.
1. Cucurbita:
A transverse section through the petiole of Cucurbita shows the following anatomical features (Fig. 5.124):
It is wavy in outline having distinct ridges and furrows and a large cavity at the centre.
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(i) Epidermis:
The single layered epidermis is made of a row of tubular cells with cuticularised outer walls. A large number of multicellular hairs are present on the epidermis.
(ii) Cortex:
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The ground cortex contains patches of collenchyma cells at the ridges. The rest of the ground tissue is composed of thin-walled parenchyma with distinct intercellular spaces. A big cavity is present at the centre.
(iii) Vascular bundles:
The vascular bundles are arranged in a ring. Individual bundles are conjoint, bicollateral and open.
2. Sunflower:
The cross-sectional outline of the petiole of sunflower (Helianthus annus of family Compositae) is concave at one side and convex at the other.
The tissue arrangement is as given (Fig. 5.125):
(i) Epidermis:
The single layered epidermis consists of tubular cells and a large number of epidermal hairs.
(ii) Cortex:
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In the ground cortex there occurs a collenchymatous hypodermis, broken by chlorenchyma here and there, internal to epidermis. The rest of ground tissue is made of isodiametric parenchyma cells with distinct intercellular spaces.
(iii) Vascular bundles:
A number of vascular bundles of different sizes occur in the form of a band. Some bundles are small and some are quite large. Every bundle is conjoint and collateral.
3. Piper Betle:
The cross sectional outline of the petiole of Piper betle of family Piperaceae is more or less heart-shaped with a concave groove at one side and convex surface at the other (Fig. 5.126).
(i) Epidermis:
The epidermis is single cell- layered with cutinised outer walls.
(ii) Cortex:
The outer zone of the ground cortex forms the collenchymatous hypodermis interrupted here and there by small patches of chlorenchyma. The rest zone is distinctly parenchymatous. Many large and small mucilage canals remain scattered throughout the ground tissue. The larger canals remain at the center.
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(iii) Vascular bundles:
Vascular bundles of different sizes occur in the form of an arc. The vascular bundles are conjoint and collateral. The xylem remains towards the centre and the phloem remains towards the periphery.
4. Waterlily:
The petiole of waterlily (Nymphaea stellata of the family Nymphaeaceae) are characterised by large air chambers, branched trichosclerides or internal hairs with calcium oxalate deposition, and scattered vascular bundles with very poorly developed xylem elements.
Transverse section of the petiole of waterlily shows the following anatomical features (Fig. 5.127):
(i) Epidermis:
The epidermis is made of a layer of chloroplast containing roundish cells with little cuticularisation on their outer walls. Unbranched multicellular hairs are usually found on the epidermis.
(ii) Cortex:
The outer zone of the ground cortex forms the 2-3 layered collenchymatous hypodermis with angular thickenings. Rest of the cortex is made of thin-walled parenchyma with large number of air chambers. Trichosclereids of peculiar shapes — often with deposition of calcium oxalate crystals — are abundantly present.
(iii) Vascular bundles:
Very poorly-developed vascular bundles of different sizes remain scattered in the ground tissues. The xylem vessels usually disintegrate and form lacunae which resemble the air chambers. The phloem elements are normally developed. The smaller vascular bundles have a single patch of phloem, and comparatively larger bundles have two patches of phloem.
