Fig. 2: Harold Wager’s photographs taken through the plant epidermis.

1—cells of the upper epidermis of Tradescantià fluminensis, 2—cells of the upper epidermis of Mesembryanthemum cordifolium, 3—cells of the lower epidermis of Mesembryanthemum cordifolium, 4—the special cells on the underside of the leaf of Mesembryanthemum cordifolium, 5—rays of light brought to a focus through the granules of mucilage. These granules interfere with the passage of light through the cells as a whole and render the image almost indistinct (Wager, 1909). Public domain image.