Electron Microscopic Investigations of the Walls of Green Algae

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Abstract
A survey of the structure of wall lamellae in the green alga Valonia ventricosa has revealed the following details. The microfibrils are not so constant in width as had previously been suggested; they vary in this dimension from about 100 A to about 350 A. The length of the shadow cast by separated microfibrils shadowed with palladium-gold or with uranium suggests that the microfibrils are flattish ribbons rather than circular cylinders. In the intermediate lamellae of the wall they are in intimate contact, probably with an interfibrillar cementing material, but in outer lamellae they become more or less widely separated. This separation is assumed to occur as a result of adjustment to size increase in the vesicle. Observation of the innermost lamella shows that the microfibrils here are arranged at random, in marked contrast to the condition in other lamellae. Here and there granular deposits on this lamella appear to be connected with the cytoplasm, and it is suggested that these may represent points in the cytoplasm associated with microfibril production. Occasional twisting of microfibrils over and around each other in most of the wall lamellae suggests most strongly that the wall and the cytoplasm are not so clearly separated during deposition as has been thought.

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