TREES 



367 



growth as a rule can endure more shade. There are also 

 some low species, as the blue beach, the dogwoods, and others, 

 that are shade loving. These shade-loving shrubs and the 

 young growth constitute 

 the underbrush, which 

 in more open forests 

 may be a veritable 

 jungle. 



In time the tree 

 reaches a period of old 

 age, when its vitality 

 begins to diminish, and 

 it is subject to the at- 

 tacks of fungi and bac- 

 teria of decay or dis- 

 ease. The effects of 

 insects, such as canker- 

 worms that eat the foli- 

 age, and the bark and 

 wood boring larvae, are 

 also more serious then. 

 The heart-wood decays, 

 perhaps, the branches 

 die from the attacks of fungi and insects, and fall. Gradually 

 the tree dies. Decay is hastened. The trunk and roots are 

 weakened, and a storm uproots or breaks down the tree. We 

 see many broken limbs, fallen tree trunks, and old stumps lit- 

 tering the forest floor. There they gradually rot and return to 

 the soil the mineral matter and to the air the gases that were 

 used in their upbuilding. In this process of decay many 

 fungi and bacteria take an active part. We see shelf fungi, 



FIG. 157. A Shelf Pore-Fungus. 



(The chief part of the fungus is inside the tree, causing 



death and decay.) 



