
THE STEM nay 
shoots. A callus formed from the main stem then starts to grow 
out over the stump, but before the stump is covered it begins 
to decay, as is clearly illustrated in Fig. 156. The decay extends 
into the wood of the main branch and trunk, with the result 
that the tree becomes hollow. For similar reasons, if a twig 
is to be cut back but not removed, the cut should be made a 
little above a bud and not in the middle or upper part of an 
internode. If a portion of an internode is left, it dies and its 
presence interferes with the closing of the callus over the wound. 

Fic. 156. Dead stumps, showing how decay may enter a tree trunk 
Budding and grafting. Budding and grafting consist in insert- 
ine a part of one plant into another in such a way that a per- 
gap p Ve p 
q 
manent union is formed and the inserted piece continues to grow. 
The part which is inserted is known as the scion, and the plant 
into which it is inserted is called the stock. The success of the 
operation depends primarily upon bringing the cambium of the 
scion into contact with that of the stock. 
Budding consists essentially in removing a small piece of bark 
with a bud and little or no wood from one plant and inserting 
it under the bark of another plant (Fig. 157). The piece in- 
serted is known as the dud. The usual method is called shield 
budding, on account of the shieldlike shape of the bud. In this 
method an oval piece of bark with a bud is cut from one twig. 
