. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 3. Carbon replica, metal-shadowed, of a beaten spruce tracheid and its associated fibrillation. Magnification 1500, inset 13,000. Fig. 4. Carbon replica, metal-shadowed, of a surface of wood tissue. The wood—Scots pine—was cut in a radial plane with a chisel prior to replication. Magnification < 1700. remain embedded in the methacrylate ic). The stripping of the fibres is sometimes dil'Hcult, cellulose tape being by no means always effective. A more successful method employs a 10 "„ solution of poly-
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 3. Carbon replica, metal-shadowed, of a beaten spruce tracheid and its associated fibrillation. Magnification 1500, inset 13,000. Fig. 4. Carbon replica, metal-shadowed, of a surface of wood tissue. The wood—Scots pine—was cut in a radial plane with a chisel prior to replication. Magnification < 1700. remain embedded in the methacrylate ic). The stripping of the fibres is sometimes dil'Hcult, cellulose tape being by no means always effective. A more successful method employs a 10 "„ solution of poly- vinyl alcohol (PVA) in water. This solution is poured onto the methacrylate cast and gradually sets to a hard film which when stripped, brings with it the embedded fibre id). In particularly stubborn cases this process can be repeated. From the negative cast so formed a robust positive replica is made in PVA. A 10 % solution of PVA in water, sufficient to form a film about mm thick, is poured onto the cast and allowed to set (e). This replica, which is a reproduction of the original fibre lying on its glass substrate, can be separated easily from the methacrylate (/). It is preshadowed with gold, palladium, and carbon is deposited on it in the usual manner. At this point a handling technique is adopted (5) that ensures that the fragile carbon replica is mount- ed intact on its grid. Briefly this technique consists of embedding the carbon replica together with the support grid in thick plastic films which are washed away after the composite arrangement has been inserted in the specimen cap and holder. Thus the delicate replica surface is at no time exposed during the manipulation of the grid and accidental damage to the replica is avoided. The only chance of damage is during the final flow-wash (a very gentle one) with chloroform. Very thin replicas of rough surfaces can be made and mounted on coarse mesh grids with confidence. For the replication of fibres, carbon fi
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