132 



GROWTH AND WORK OF PLANTS 



Fig. 100. 



Spawn of the polyporus as it makes its way 

 through the wood of the tree. 



and forms the well-known bracket fungi so common in the forests, 

 or in the case of other species forms the toadstools or mushrooms 

 often seen growing from the wounds of trees. 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 myce- 

 lium disintegrates the cellulose 

 and wood.* After these have 

 finished their work, other spe- 

 cies 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. 



216. 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 XXVI). 



217. 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 

 heated to kill the germs of fungi and bacteria and then sealed in 

 " cans " to shut out the air and the entrance of germs, are pre- 



* 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. 



