[Illustration: FIG. 164.—CURRANT CUTTING.] =The Graft.=—_When the cutting is inserted in a plant rather than in the soil, it is a graft_; and the graft may grow. In this case the cutting grows fast to the other plant, and the two become one. When the cutting is inserted in a plant, it is no longer called a cutting but a =scion=; and the plant in which it is inserted is called the =stock=. Fruit trees are grafted _in order that a certain variety or kind may be perpetuated_, as a Baldwin or Ben Davis variety of apple, Seckel or Bartlett pear, Navel or St. Michael orange. _Plants have preferences as to the stocks on which they will grow; but we can find out what their choice is only by making the experiment._ The pear grows well on the quince, but the quince does not thrive on the pear. The pear grows on some of the hawthorns, but it is an unwilling subject on the apple. Tomato plants will grow on potato plants and potato plants on tomato plants. When the potato is the root, both tomatoes and potatoes may be produced, although the crop will be very small; when the tomato is the root, neither potatoes nor tomatoes will be produced. Chestnut will grow on some kinds of oak. In general, one species or kind is grafted on the same species, as apple on apple, pear on pear, orange on orange. _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 scion and of the stock must come together_. Therefore the scion is set in the side of the stock. There are many ways of shaping the scion and of preparing the stock to receive it. These ways are dictated largely by the relative sizes of scion and stock, although many of them are matters of personal preference. The underlying principles are two: securing _close contact_ between the cambiums of scion 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 scion is firmly inserted. Fig. 165 shows the scion; Fig. 166, the scions 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.