60 Practical Farming 



growth of the following season starting with large and thin- 

 walled cells and gradually growing thicker-walled toward 

 the close of the season of growth. 



The ring-like appearance gives us the means for count- 

 ing the age of the tree. Growth is added to the tree in 

 circles of cells something after the manner of building a 

 house by adding brick after brick, only that in the tree 

 the brick-maker and the mason live inside the bricks and 

 from their own substance construct the walls around them. 

 In the first stages of growth, as between the bark and 

 the wood, these cells are all in communication with each 

 other, so that materials can be transported up or down 

 throughout the whole increasing tissue of the cells, and 

 their becoming more woody cuts off each cell to itself, 

 and the living matter in each cell goes on thickening the 

 walls around it till its substance is entirely used up, and 

 in the completed wood there is no life left. It is now 

 heart wood, dead wood, and remains simply as a support 

 to the tree, while the life goes on circling around it and 

 gradually adding more completed wood to the heart. 

 That this heart wood is no longer of use to the tree except 

 as a support is well shown by the fact that the heart may 

 decay and the tree become hollow and the growth still 

 goes on uninterrupted. But cut off the sap wood, and 

 the tree at once dies. 



There is, however, another class of plants 

 C^sses^of"^^ in the stems of which we see none of this 

 Plants ring-like growth, but the whole stem is 



filled with a multitude of long fibers growing 

 through a softer aggregation of thin-walled cells. We do 

 not find this character of growth in trees till we reach the 



