ECONOMIC IMPORTANCE OF FUNGI 



303 



the Department of Agriculture, 

 importation of every spe- 

 cies of the genus Pinus has 

 been forbidden from all 

 European countries and lo- 

 calities. In March, 1916, 

 the Federal Horticultural 

 Board requested all nursery- 

 men in the eastern United 

 States not to ship white 

 pine, gooseberry or currant 

 stock into the Rocky Moun- 

 tain and Western white pine 

 forest areas. 



288. Timber-destroying 

 Fungi. Everyone recalls 

 the "shelf-fungi," so often 

 seen growing on the trunks 

 of trees (Fig. 223). These 

 forms are the fruiting bodies 

 of the fungus, while the my- 

 celium ramifies through the 

 wood, often in such quan- 

 tities as to form the "punk," 

 formerly much used in set- 

 ting off fireworks. The soft 

 fungal threads are enabled 

 to make their way through 

 the hard woody tissue by 

 means of an enzyme which 

 they secrete. The enzyme 

 softens and dissolves the cell-walls 



Since July i, 1915, the 



FIG. 223. A shelf-fungus (Pomes 

 applanatus] on sugar maple. 



of the wood, thus 



