_The forming, growing tissue of the stem_ (on the plants we have been discussing) is the =cambium= (Chap. X), _lying on the outside of the woody cylinder beneath the bark_. In order that union may take place, _the cambium of the cion and of the stock must come together_. Therefore the cion is set in the side of the stock. There are many ways of shaping the cion and of preparing the stock to receive it. These ways are dictated largely by the relative sizes of cion and stock, although many of them are matters of personal preference. The underlying principles are two: securing _close contact_ between the cambiums of cion and stock; _covering the wounded surfaces_ to prevent evaporation and to protect the parts from disease. On large stocks the commonest form of grafting is the =cleft-graft=. The stock is cut off and split; and in one or both sides a wedge-shaped cion is firmly inserted. Fig. 165 shows the cion; Fig. 166, the cions set in the stock; Fig. 167, the stock waxed. It will be seen that the lower bud--that lying in the wedge--is covered by the wax; but being nearest the food supply and least exposed to weather, it is the most likely to grow: it will push through the wax. =Cleft-grafting= _is practiced in spring, as growth begins. The cions are cut previously, when perfectly dormant, and from the tree which it is desired to propagate._ The cions are kept in sand or moss in the cellar. Limbs of various sizes may be cleft-grafted,--from one half inch up to four inches in diameter; but a diameter of one to one and one half inches is the most convenient size. All the leading or main branches of a tree top may be grafted. If the remaining parts of the top are gradually cut away and the cions grow well, the entire top will be changed over to the new variety. [Illustration: FIG. 165.--CION OF APPLE.] [Illustration: FIG. 166.--THE CION INSERTED.] [Illustration: FIG. 167.--THE PARTS WAXED.] Another form of grafting is known as =budding=. In this case a single bud is used, and it is slipped underneath the bark of the stock and securely tied (not waxed) with soft material, as bass bark, corn shuck, yarn, or raffia (the last a commercial palm fiber). Budding is performed _when the bark of the stock will slip or peel_ (so that the bud can be inserted), and _when the bud is mature enough to grow_. Usually budding is performed in late summer or early fall, when the winter buds are well formed; or it may be practiced in spring with buds cut in winter. In ordinary summer budding (which is the usual mode) the “bud” or cion forms a union with the stock, and then lies dormant till the following spring, as if it were still on its own twig. Budding is mostly restricted to young trees in the nursery. In the spring following the budding, the stock is cut off just above the bud, so that only the shoot from the bud grows to make the future tree. This prevailing form of budding (shield-budding) is shown in Fig. 168.