418 



TEXTBOOK OF BOTANY 



Fig. 193. Parts ot plants used in grafting: A, stump or crown grafting; B, piece- 

 root grafting; C, C budding; D, bridge grafting; E, approach grafting. 



and form wound tissue, or callus. In successful grafts, new cambium cells 

 develop from some of the cells in the callus and unite the cambiums of 

 stock and scion. The new xylem and phloem tissues formed become con- 

 tinuous; and water, salts, sugar, hormones, and other soluble substances 

 move across the junction. 



If this union of tissues fails to occur, the scion dies. If the union is 

 not well formed, the movement of water and salts to the scion and of 

 sugar to the stock is restricted and growth of the whole plant is slow. 



The fundamental features of bud grafting are similar to those of twig 

 grafting. If the bud of a peach tree is grafted in place in late summer, 

 healing occurs within a few weeks, but the bud remains donnant until 

 the following spring when a branch develops from it in the usual way. To 

 insure the growth of the grafted bud, the stem is cut off just above it to 

 remove the source of apical dominance. Branches will develop from the 

 buds the same year the graft is made, if the buds formed the previous 

 year are collected in winter and kept on ice until the graft is made in 

 June. 



Established grafts are commonly obtained onlv among related plants, 

 as among \'arieties of peach, apricot, and plum, or among varieties of 



