THE IIYMENOMYCETES 



265 



Many of the pore fungi are perennial, increasing in size from 



year to year by adding new 

 layers of growth outside of 

 the old. The bracket or toad- 

 stool is merely the fructifica- 

 tion which receives its nour- 

 ishment from an extensive 

 mycelium growing in the 

 wood, and under the bark of 

 trees, or in the soil. Many 

 of the pore fungi are very 

 destructive parasites, greatly 

 injuring and sometimes kill- 

 ing forest trees. They may 

 cause great injury to growing 

 timber. 1 Most of the pore 

 fungi are, however, sapro- 

 phytic in their manner of 

 life. 



The tooth fungi. The tooth fungi (family Hydnacece) are less 

 common than the pore and 

 gill fungi. Some of them have 

 bracket forms, and some are 

 toadstools (Fig. 236). The 

 fruiting surface is distrib- 

 uted over tooth or spine-like 

 processes. 



The gill fungi. The gill 

 fungi (family Agaricacecc} in- 

 clude most of the toadstool 

 and mushroom forms (Fig. 

 237). A toadstool consists of FlG< 2 36. A tooth fungus (Hydnum) 



1 See von Schrenk, "The Decay of Timber and Methods of Preventing 

 It," United States Department of Agriculture, Bureau of Plant Industry, 

 Bulletin 14, 1902. 



FIG. 235. A pore-bearing toadstool 

 (Boletus) 



