Thursday, 29 April 2021

In Cucurbita the pith degenerates largely to cavity

 In Cucurbita the pith degenerates largely to cavity



Pith or Medulla : It constitutes the central part of the stem. Pith consists of rounded, oval or polygonal parenchyma cells. Intercellular (8) spaces are abundant, The cells store food materials and waste products. In Cucurbita the pith degenerates largely to form cavity. 

A central Reasons of Identification : (i) Occurrence of multicellular hair epidermis, over (ii) Collenchymatous hypodermis. (iii) Wedge- shaped conjoint collateral and open vascular bundles arranged in a single ring. (iv) Prèsence of bundle caps or sclerenchymatous pericycle over vascular bundles, (v) Endarch xylem.

 1.1.4 Internal Structure of Monocot Stem : Monocot stem possesses only primary structure. It is usually circular in outline. The stem may be solid (e.g., Maize) or fistular (e.g. Grass). Monocot stem does not have differentiation of various components of ground tissue system.

 Vascular bundles are also scattered. The different components of monocot stem from outside towards inside are epidermis, hypodermis, ground tissue and vascular strand.

 Epidermis : It is uniseriate outer protective layer of living parenchymatous cells. The cells are rectangular-barrel shaped in outline. The outer walls are cutinised and silicified. Distinct layer of cuticle with or without silica incrustation is present on the outer side. At places the epidermis bears stomata. Each stomate or stoma is surrounded by two dumb.

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