_Pot layering_, _circumposition_, _air layering_ and _Chinese layering_ are terms applied to the rooting of rigid stems by means of surrounding them, while in their natural position, by earth or moss, or similar material. The stem is wounded--commonly girdled--and a divided pot or box is placed about it and filled with earth (Fig. 22). The roots start from above the girdle, and when they have filled the pot the stem is severed, headed back, and planted. Pot layering is practiced almost exclusively in greenhouses, where it is possible to keep the earth uniformly moist. But even there it is advisable to wrap the pot in moss to check evaporation from the soil. Some plants can be readily rooted by wrapping them with moss alone. Pot layering is employed not only for the purpose of multiplying plants, but in order to lower the heads of "leggy" or scraggly specimens. The pot is inserted at the required point upon the main stem, and after roots have formed abundantly the top may be cut off and potted independently, the old stump being discarded. [Illustration: Fig. 23. Layering pot.] [Illustration: Fig. 24. Layering cone.] [Illustration: Fig. 25. Layering cup.] [Illustration: Fig. 26. Layering cup.] [Illustration: Fig. 27. Compound layering pot.] The French have various handy devices for facilitating pot layering. Fig. 23 shows a layering pot, provided with a niche in the side to receive the stem, and a flange behind for securing if to a support. Fig. 24 represents a layering cone. It is made of zinc or other metal, usually four or five inches high, and is composed of two semi-circular wings which are hinged on the back and are secured in front, when the instrument is closed, by means of a hinge-pin. A cord is inserted in one side with which to hang it on a support. A cup or pot with a removable side is also used. This is shown open in Fig. 25 and closed in Fig. 26. An ingenious compound layering pot is shown in Fig. 27. The main stem or trunk of the plant is carried through the large opening, and the branches are taken through the smaller pots at the side. Kier's layering boxes or racks are shown in Figs. 28 and 29. The trays are filled with earth and the branches are laid in through the chinks in the border and are treated in the same manner as ordinary out-door layers. These racks supply a neat and convenient means of increasing greenhouse plants which do not readily strike from cuttings. [Illustration: Fig. 28. Kier's layering rack.] It is well to bear in mind that when layers do not give strong plants, they can be divided into portions and treated as ordinary cuttings. This is an important operation in the case of rare varieties which are multiplied by means of soft or green layers, as some of the large-flowered clematises and grapes. The weak small plants are handled in a cool greenhouse or under frames, usually in pots, and they soon make strong individuals. [Illustration: Fig. 29. Kier's circular layering rack.] CHAPTER IV.