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

The microfibrillar framework of parenchymatous walls in Cucurbitawas observed in petioles treated so as to remove various non-cellulosiccell wall components. Such extraction typically results in separationof the microfibrillar components into concentric lamellae. Thenumber and thickness of these lamellae vary according to theage and type of cell wall. The microfibrils appear to be orientatedwithin the plane of their lamellae but the orientation may varyin successive lamellae, and in many walls the crossed polylamellatecondition was detected. The collenchyma—and the outerepidermal cell walls show an alternation of lamellae with almostvertical microfibrils with those with a practically transverseorientation. In ordinary parenchymatous walls the alternationis not so extreme and is revealed only by the occasional presenceof the ‘herring bone pattern’ in non-radial sections.As a rule the lamellae are continuous around the circumferenceof a cell though individual lamellae may vary in thickness andsometimes appear to ‘fade out’. The present observationssuggest that growth of the primary wall occurs by depositionof microfibrils in successive lamellae thus confirming the basicpremise of the multinet theory of growth.