404 



PLANT PHYSIOLOGY 



cut off at the crown, and a small cutting of an improved variety 

 is then grafted upon the remaining stump. 



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 drying out of the junction, it is sealed with graft- 



i'-:^ 



Fig. 126. — Methods of budding and grafting. Left, budding; center, whip graft- 

 ing; right, cleft grafting {after Brown.) 



ing wax and sometimes firmly bandaged. Instead oJT a whole 

 cutting, very often only a bud with a small section of adjacent 

 bark and wood is used for propagation purposes. This shieldlike 

 cutting is inserted into a slit made in the bark of the stock. 

 This method is known as "budding" (Fig. 126). Various other 

 methods of grafting and budding are known, but these will not 

 be discussed here. 



With all the methods of this type of propagation, it is most 

 important to ensure the closest contact between similar tissues 

 of the same age of the stock and scion, as only such tissues can be 

 joined together by growth. The callus plays the part of an 

 intermediary agent in the process of subsequent differentiation 

 of vessels and sieve tubes, which serve to connect the correspond- 

 ing elements of both plants. In grafting, the contact of the 



