140 GROWTH AND WORK OF PLANTS 



Some of these same wood-destroying fungi grow on the dead 

 logs, stumps and branches forming the brackets or mushrooms 

 which are the fruiting bodies. The mycelium disintegrates the 

 cellulose and wood.* After these have finished their work, other 

 species come in and carry the disintegration farther, and so on 

 until the wood is reduced to humus when still other species grow- 

 on this. The dead leaves are attacked by still other species 

 and by a similar series of fungus forms are reduced to humus. 



Fig. 102. 

 Spawn of the polyporus as it makes its way through the wood of the tree. 



218. The molds which are also fungi, are, many of them, 

 saprophytic also. They grow on fruits, preserves, old bread and 

 isolated plant parts which are not humus (see the bread mold in 

 Chapter XXVIII). 



219. Decay. All decay is due to the action of living organisms, 

 chiefly fungi and bacteria. If these organisms could be excluded 

 from fruits, vegetables, preserves, meats, or any plant or animal 

 part, these organic substances would be preserved indefinitely 

 and if exposed to the air would simply dry out. Dried beef is 

 rendered safe from decay because the percentage of moisture is 

 insufficient for the growth of bacteria. Fruits which are first 



* The mycelium of some of the bracket fungi (Polyporus mollis, for ex- 

 ample) dissolves only the cellulose of the wood leaving the xylogen, while 

 others (Trametes pini, for example) dissolve only the xylogen, leaving the 

 pure cellulose intact in which the xylogen was infiltrated. 



