The forming, growing tissue of the trunk is the cambium, lying on the outside of the woody cylinder, beneath the bark. In order that union may take place, the cambium of the cion and the stock must come together. Therefore, the cion is set in the side of the stock. I once knew a man who believed that everything was designed for some useful purpose. The hole in the pith bothered him, until he discovered that a cion just filled it. He grafted his trees accordingly; but the experiment was productive of nothing except pithy remarks. [Illustration: _Fig. 266. Cleft-graft. One-half natural size._] 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 mere personal preference. The underlying principles are two: see that there is close contact between the cambiums of cion and stock; cover the wounded surfaces to prevent evaporation and to protect the parts from disease. [Illustration: _Fig. 267. The graft waxed._] On large stocks the common 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. 265 shows the cion; Fig. 266, the cions set in the stock; Fig. 267, 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 pushes through the wax. [Illustration: _Fig. 268. Shield-budding. One-half natural size._] The wax is made of beeswax, resin, and tallow. The hands are greased, and the wax is then worked until it is soft enough to spread. For the little grafting which any school would do, it is better to buy the wax of a seedsman. However, grafting is hardly to be recommended as a general school diversion, as the making of cuttings is; and this account of it is inserted chiefly to satisfy the general curiosity on the subject. But we hope that now and then a youngster will make the effort for himself, for nothing is more exciting than to make a graft grow all by one's self. Cleft-grafting is done 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 inch 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 scions grow well, the entire top will be changed over to the new variety in three or four years. Each cion may be a different variety; but there is no difference in the operation or the treatment of the tree.