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 (Fames 
applanatus) on sugar maple. 
of the wood, thus 
