Observations on the Fine Structure of Plant Cell Walls II. The Microfibrillar Framework of the Parenchymatous Cell Wall in Cucurbita

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Abstract
The microfibrillar framework of parenchymatous walls in Cucurbita was observed in petioles treated so as to remove various non-cellulosic cell wall components. Such extraction typically results in separation of the microfibrillar components into concentric lamellae. The number and thickness of these lamellae vary according to the age and type of cell wall. The microfibrils appear to be orientated within the plane of their lamellae but the orientation may vary in successive lamellae, and in many walls the crossed polylamellate condition was detected. The collenchyma—and the outer epidermal cell walls show an alternation of lamellae with almost vertical microfibrils with those with a practically transverse orientation. In ordinary parenchymatous walls the alternation is not so extreme and is revealed only by the occasional presence of the ‘herring bone pattern’ in non-radial sections. As a rule the lamellae are continuous around the circumference of a cell though individual lamellae may vary in thickness and sometimes appear to ‘fade out’. The present observations suggest that growth of the primary wall occurs by deposition of microfibrils in successive lamellae thus confirming the basic premise of the multinet theory of growth.

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