126 PLANT BIOI.OCY 



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 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 evapora- 

 tion 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 



