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The Growth of Stems 



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157 



Southern Lumbertnan 



Figs. 92 and 93, Patterns formed by annual rings and medullary rays. The board at 

 the left is longleaf yellow pine, and the one at the right "quarter-sawed" white oak. In 

 the pine the markings are due to the rings. In the oak the edges of the rings appear as 

 longitudinal lines and the pith rays as irregular cross markings. Can you explain exactly 

 how each board was cut to show these markings ? 



Heartwood and sapwood. As the trunks of trees increase in 

 thickness, all the cells toward the center of the stem gradually die. 

 The wood usually changes in color after the death of these cells. 

 In a peach tree only the outer three or four annual rings may be 

 alive. In a walnut trunk 2 feet in diameter, all but the outer 

 2 inches may be dead. The dead wood still helps to support the 

 enormous weight of the tree top, but it has nothing to do with the 

 conduction of water and substances in solution. This inner dead 

 wood is called the heartwood; the outer living wood is called the 

 sapwood. The heartwood in many species of trees is much more 

 valuable than the sapwood for lumber, because of its color and 

 greater durability. 



Grafting and budding. In the propagation of many varieties of 

 fruit trees it has been found that seeds are not satisfactory. 

 Most of our cultivated fruit trees are so highly variable that their 

 seedlings are not like the parent plants in quality of fruit. Horti- 



