The Seniors of the Forest 281 



tissue. The oldest wood is at the centre of the 

 trunk, and the newest is just beneath the bark 

 (Fig. 78). 



But in many cone-bearers and notably in the 

 white pine, the heart-wood undergoes little altera- 



FIG. 78. Crosswise section of the trunk of a fir-tree, showing 



growth-rings. 

 (From the Vegetable World.) 



tion as the tree matures, and it can resume the 

 industry of former years, if necessary, and conduct 

 water upward toward the thirsty leaves. Indeed 

 so great is its versatility that it can make shift to 

 fill, after a fashion, the offices of young wood and 

 of bark, so that plant-fluids still ascend and 

 descend slowly even in a girdled pine. 



