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H. W. EMERTON, D. H. PAGE AND J. WATTS 



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, of fibrils 

 that come away taut from the upper surface of the 

 fibre. Such fibrils, examples of which may be seen 

 in fig. 1, are evidently completely embedded in the 

 plastic matrix that constitutes the first stage of the 

 replica process, break during the stripping of the 

 fibre and are consequently not entirely replicated. 



We have also investigated the possibility of ap- 

 plying reflection electron microscopy to the study 

 of paper surfaces. Fig. 3 shows a replica of the surface 

 of a tissue paper made for use as a dielectric in con- 

 densers. Notwithstanding the very heavy and pro- 

 longed beating to which the fibres are subjected to 

 produce this type of paper — a treatment which is 

 said to reduce the pulp to a gel — it is clear that 

 some of the fibres have retained their general integ- 

 rity. 



This micrograph in particular brings out one of the 



