LAYERS are portions of the branches of a plant that have been induced to throw out roots, and which can thus set up an independent existence if removed from the parent tree. This mode of propagation is a very natural one, and was probably an accidental discovery. In its traits, it is the reverse of the mode we have just been considering. Here the branch emits roots, instead of the root emitting branches, as in the case of the sucker. Layering is frequently resorted to as a mode of propagation, it is very simple, easily performed, and, with some species, very certain in its results. Some plants will root readily if merely placed in contact with the ground, or very slightly covered with soil; others require some artificial interference, such as ringing, or twisting, or slitting. The raspberry, known as the _Rubus occidentalis_ or Black-cap, belongs to the first class, and it even places itself in contact with the soil by recurving its branches so as to bring the tips to the earth, where they strike root, and make new plants. The grape comes under the second category, needing only a little assistance, and it is multiplied to a considerable extent in this manner. In the spring, the vines are laid out in a little shallow trench, and pegged down closely; as the buds burst, they throw up shoots which are trained vertically by tying them to sticks, and as soon as these shoots have acquired a certain degree of maturity and firmness, the mellow earth is drawn up to them and they emit a beautiful system of roots, and by the fall they form very fine plants, (fig. 3). The layered branch is then taken up and the several plants are separated, when it will be found that the best roots are chiefly from the lower joints of the new wood, rather than from the old canes that were laid down in the spring. [Illustration: Fig. 3.--PROPAGATING THE GRAPE BY LAYERING.] [Illustration: Fig. 4.--LAYERING THE QUINCE.] [Illustration: Fig. 5.--STOOL LAYERING THE QUINCE.]