. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . All the micrographs are of solid replicas. The scale ellipses are 25 microns in diameter. The angles of illumination and viewing are 5" and 12 respectively. Fig. 1. Reflection electron micrographic montage (considerably reduced) of a beaten spruce sulphite tracheid. Fig. 2. Reflection electron micrograph of a thin-walled spruce sulphite tracheid, heavily beaten. Fig. 3. Reflection electron micrograph of the surface of a tissue paper made from hemp and flax fibres. is not directly apparent from examination in
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . All the micrographs are of solid replicas. The scale ellipses are 25 microns in diameter. The angles of illumination and viewing are 5" and 12 respectively. Fig. 1. Reflection electron micrographic montage (considerably reduced) of a beaten spruce sulphite tracheid. Fig. 2. Reflection electron micrograph of a thin-walled spruce sulphite tracheid, heavily beaten. Fig. 3. Reflection electron micrograph of the surface of a tissue paper made from hemp and flax fibres. is not directly apparent from examination in the light microscope which gives only a plan view. The form of the twist in the middle of the tracheid in fig. 1 would also be difficult to appreciate from examination in the light microscope. In both micrographs there is evidence of promi- nent, more or less transverse, fibrils on the surface of the tracheids. Care is needed in interpreting these. In the first place the image is foreshortened. (An impression of this foreshortening is given by the scale ellipse (5) which must be thought of as a circle lying in the plane of the substrate.) A linear feature inclined to the plane containing the line of sight and the normal to the substrate is imaged at an angle exceeding the true value (8) and hence a fibril lying in this plane appears more nearly transverse. Further- more, the width of the fibrils cannot be readily as- sessed for the contrast scheme does not permit meas- urements in this direction to be made with accuracy because of the foreshortening and loss of informa- tion in shadow. The apparently transverse fibrils in these micrographs are, however, thought to be part of the outer secondary wall that has been modified by the sulphite digestion to which these cells have been subjected but further work is required to establish this. The only common artefact arising from the use of solid replicas for the examination of pulp fibres is the incomplete replication, in some cases,
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