Notes on the Internal structure of stem of cucurbita maxima

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The outline of a cross section is wavy having ridges and furrow.

Epidermis: It consists of a single layer of cells. The epidermis is covered by a thin layer of cuticle. Multi cellular hairs arise from epidermal cells.

Cortex: It occurs below the epidermis and extends up to the pericycle. It consists of the outer hypodermis, the middle general cortex and the lowermost endodermis.

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(i) Hypodermis: It occurs below the epidemis, consists of 6-7 layers of collenchymatous cells in the ridges and 2-3 layers in the furrows.

(ii) General cortex: It forms a narrow zone consisting of 2-3 layers of chlorenchymatous cells.

(iii) Endodermis: It is the innermost layer of the cortex lying immediately outside the pericycle. It consists of barrel shaped cells and is wavy in outline, the cells contain starch grains.

Pericycle: It consists of 3-4 layers of thick-walled, lignified, polygonal, sclerenchymatous cells. The general out-line of this layer is also wavy.

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Vascular bundles: The vascular bundles are arranged in two rings. They are conjoint, bicollatral and open type. The outer rings of vascular bundles are comparatively small in size and occur opposite to ridges. The inner ring consists of larger vascular bundles which occur below the furrows. Each vascular bundle consists of

(i) Xylem

(ii) Two strips of cambium and

(iii) Two patches of phloem.

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Phloem: Phloem occurs in two patches. The outer phloem is towards the periphery and the inner phloem is towards the pith. The outer phloem is plan convex and the inner one is semi lunar in shape. Phloem consists of sieve tubes, companion cells, phloem fibers and phloem parenchyma.

Cambium: Combium occurs in two strips-the outer and the inner one on each side the xylem. The cells are rectangular and thin walled.

Xylem: It is located in between the two cambium patches. It consists of vessels tracheids, wood fibers and wood parenchyma. Xylem is end arch in nature.

Pith: It is a hollow cavity.

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