68 



STRUCTURE OF THE STEM 



As the bud develops into a branch, the few bundles which it 

 originally possessed increase greatly in number, and at length, 

 as the branch grows, form a cylinder of 

 wood which cuts across the annual rings, 

 as shown in Fig. 69. This interruption to 

 the rings is a knot, such as one often sees 

 in boards and planks. If the branch dies 

 long before the tree does, the knot may 

 be buried under many rings of wood. What 

 is known as "clear" lum- 

 ber is obtained from trees 

 that have grown in a 

 dense forest, so that the 

 lower branches of the 

 larger trees were killed 

 by the shade many years 

 before the tree was felled. 

 In pruning fruit trees 

 a knot in a tree trunk or shade trees the 



R, cut-off end of stick, branches which are re- 

 showing annual rings ; ^ ^ , ^ -. 



K, knot formed by m0ved should be Cut 



growth of a branch. close to the trunk. If 



After Roth A . . . , 



this is done, the growth 

 of the trunk will bury the scar before decay 

 sets in. 



83. Grafting. When the cambium layer 

 of any vigorously growing stem is brought in FIG. 70. Grafting 

 contact with the same layer in another stem At the left scion and 

 of the same kind or a closely similar kind of 

 plant, the two may grow together to form a 

 single stem or branch. This process is called 

 grafting, and is much resorted to in order to 

 secure apples, pears, etc., of any desired kind 

 (Fig. 70). A twig known as the scion from a plant of the chosen 

 variety may be grafted upon another individual of similar kind 



FIG. 



Formation of 



stock are shown 

 ready to be united ; 

 at the right they are 

 joined and ready to 

 cover with grafting 

 wax. After Perci- 

 val 



