REPRODUCTION 



363 



If the stock and the scion are of the same diameter, the oblique 

 surface of the one is placed over a similar surface of the other with 

 the purpose of joining them by growth. This method is called 

 "whip grafting." If the scion is much thinner than the stock, 

 then cleft grafting is resorted to. The stock is split in two and 

 the scion, cut to a sharp wedge, is inserted into the cut. To avoid 

 a drying out of the junction it is sealed with grafting wax and 

 sometimes firmly bandaged. Instead of a whole cutting, very 

 often only a bud with a small section of adjacent bark and wood is 

 used for propagation purposes. This shield-like cutting is inserted 



Fig. 151. — Methods of budding and grafting. Left, budding; center, whip graft- 

 ing; right, cleft grafting (after Brown.) 



into a slit made in the bark of the stock. This method is known as 

 "budding" (Fig. 151). Various other methods of grafting and 

 budding are known, but these will not be discussed here. 



In all the methods of this type of propagation it is most impor- 

 tant to ensure the closest contact between the cambium region and 

 tissues of the same age of the stock and the scion, as only such tis- 

 sues may be joined together by growth. The callus plays the part 

 of an intermediary agent in the process of subsequent differen- 

 tiation of vessels and sieve tubes, which serve to connect the 

 corresponding elements of both plants. In grafting, the contact 

 of the phloem elements is of especial importance. As has been 

 seen, it is these elements which are the centers where the callus 



