Page:Popular Science Monthly Volume 31.djvu/660

642 plane, such as is represented magnified in Fig. 4, microscopically examined, will show that the whole substance is made up of minute, many-sided cells about 1/750 of an inch in diameter, and about twice as long, the long way of the cells being disposed radially to the trunk. The walls of the cells are extremely thin, and yet they are wonderfully impervious to liquids. Looked at by reflected light, if



the specimen be turned, bands of silvery light alternate with bands of comparative darkness, showing that the cells are built on end to end in regular order. The vertical section (Fig. 5) shows a cross-section of the cells looking like a minute honey-comb. In some specimens large numbers of crystals are found, and are readily distinguished by the aid of polarized light. Minute though they are, they are very numerous



and hard, and it is partly to them that is due the extraordinary rapidity with which cork blunts the cutting-instruments used in shaping it. Cork-cutters always have beside them a sharpening-stone, on which they are obliged to restore the edges of their knives after a very few cuts; and the machines we have described are for the same