THE GROWTH OF WOOD-ROTTING FUNGI. 



25 



some take only the sugar and starcli, and leave the cell walls nearly 

 mtact; others dissolve only the celluloso, others the lignm, and 

 still others take all indiscriminately. The amount of stored food 

 material present in the cell cavities of a livin<j; tree varies much with 

 the season, at least in the temperate climates. It has been found (hat 

 trees tend to store food material in large quantities in late summer 

 and fall; in winter these supplies remain practically uniform in quan- 

 tity; in spring, when the new growth is formed, they are rapidly and 

 practically completely used up, the insoluble starch being changed 

 into the solul)le sugars. The sapwood is much richer in stored food 

 matter than is the heart- 

 wood, which usually does 

 not contain food mate- 

 rials in large quantities 

 at any time. This fact 

 partly explains the 

 greater resistance of 

 heartwood in general to 

 the attacks of these 

 fungi. The change of 

 the insoluble material 

 into some soluble form in 

 the spring explains the 

 fact that sapwood cut in 

 spring or early summer 

 usually rots very quickly, 

 while the same wood cut 

 in the winter does not rot 

 so cjuickly, the soluble 

 substances contained in 

 the spring being much 



more readily attacked by Fig. 3.— Lower end of telephone pole, showing decay at sur- 

 the funo"i than the insolu- face of ground while it is practically soiuid a short distance 

 , . alcove. 



ble ones present in winter. 



Air supply. — Wood-rotting fungi are living organisms and need a 

 certain amount of oxygen. Many bacteria are able to live beneath 

 the surface of liquids, and obtain their ox3"gen from the li({uid itself, 

 but the wood-rotting fungi seem to be unable to do tliis, and must 

 have free access to the atmospheric oxygen in order to exist in a nor- 

 mal manner. Hence, cutting off the air supply stops their growth, 

 and even kills them if continued for a sufficient length of time. This 

 fact explains why wood remains sound for hundreds of years when 

 buried, or when lying on the bottoms of streams and lakes. The 

 rafting of timber is said to have a marked effect in preventing decay, 

 and this effect may probably be partly explained m the same way, 



. 214 



