238 NATURE STUDY REVIEW [9:8— Nov., 1913 



mahogany color and P. sulphureus a sulphur yellow species is quite 

 as conxmon. While many of the shelf fungi live only on dead 

 wood, there are several species which attack living trees and do 

 great damage. Their spores enter the tree through a wound in the 

 bark ; and from the spores thus planted develops the mycelium, the 

 fungus-threads which push directly into the heart of the wood, 

 getting nourishment from it as they go. They push in radially and 

 then grow upward and downward weakening the tree where it 

 needs its strength to withstand the onslaught of the wind. Some- 

 times these threads grow into the cambium layer, which is the liv- 

 ing ring encircling the tree trunk, and kill the tree. In any case, 

 they are likely to shorten the life of the tree by many years. 



After the fungus threads are thoroughly established in the tree, 

 they again seek a wound in the protecting bark where they may 

 push out and produce the fruiting organ, which we call the bracket. 

 This bracket is at first very small and is composed of a layer of 

 honeycomb cells opening below, cells so small that we can only see 

 their openings with a lens. In each of these cells, spores are 

 developed. Next year another layer of cells grows beneath this 

 first bracket and extends out beyond it. Thus, each year an addi- 

 tion is made, so that the bracket grows thicker and its upper surface 

 is marked with concentric rings around its point of attachment. 

 Some of these bracket fungi reveal their age to us when we cut 

 down through them and count the layers 



When once the mycelium of such a fungus becomes established 

 the life of its tree host is doomed and the lumber is made worthless. 

 Sometimes a tree heals its wounds, and if there are no fresh bruises 

 made, the fungus is imprisoned within and never produces a 

 fruiting organ. However, its deadly work for the tree is accom- 

 plished. 



As soon as a tree is bruised or cut, the wound should be painted 

 or covered with a coat of tar. If the wind breaks a branch the 

 splinters left hanging should be sawed off, leaving a smooth stimip, 

 and this should be painted. While ordinary paint if renewed each 

 year will suffice, experiments show that a good coat of tar is a better 

 protection. 



This lesson should be given when a tree is found on which a shelf 

 fungus is growing. The tree itself should be carefully studied, and 

 then the fungus itself be made the subject of the lesson. The fol- 

 lowing are the topics for the children's observations: 



