126 BEGIXNERS' BOTANY 



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, grozving- tissiie of tlic stem (on the plants 

 we have been discussing) is tJie cambium (Chap. X), lying 

 on the 07itsidc of the zvoody cylinder beneath the bark. In 

 order that union may take place, t}\e cambium of the scion 

 and of the stocl' 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. Tlie underlying principles are two: 

 securing close contact between the cambiums of scion and 

 stock; covering the tvouncled 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 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. 



Cleft-grafting is practised in spring, as groiuth hegins. 

 The scions are cut previously, when perfectly dormant, and 

 from the tree which it is desired to propagate. The scions 

 are kept in sand or moss in the cellar. Limbs of various 



