TIMBER STORAGE IN THE EASTERN AND SOUTHERN STATtTS. 3 



rials readily available to the fungus and whose walls are thinner 

 than those of the wood fibers and hence more readily penetrated. 



The growth of the mycelium is conditioned by four factors: 

 (1) The presence of satisfactory food supplies, (2) a suitable amount 

 of moisture in the wood, (3) a temperature favorable for growth, 

 and (4) at least a small supply of air to furnish the necessary oxygen. 



Food supplies. — The mycelium, being a living, growing plant, 

 must have nourishment for growth, and so utilizes for tMs purpose 

 various constituents of the wood substance. These consist of the 

 different compounds which go to make up wood tissue, the celluloses 

 and ligno-celluloses being utilized as well as sugars, starches, and 

 certain organic acids. To break down the woody tissues, w^hich are 

 chemically very complex, and thus render them assimilable to the 

 fungus, certain imperfectly understood chemical substances (en- 

 zyms or ferments) are secreted by the organism. These act upon 

 the wood substance, reducing it to simpler nutritive compounds. A 

 number of these ferments have been isolated and studied by various 

 investigators and their physiological and chemical action deter- 

 mined. They are quite specific in their action; different substances 

 which enter into the composition of wood require different ferments 

 to disorganize them. In general, however, the wood-destroying 

 fungi are well supplied with the ferments necessary to produce seri- 

 ous disintegration of most of the constituents of woody tissues. 



Moisture. — A considerable amount of moisture is necessary for 

 rapid decay. Timber in an air-dry condition during dry weather 

 will not ordinarily be affected, but during periods of rainy weather, 

 when the atmospheric humidity is high, fungous infections may 

 become serious. In highly humid stagnant air a surface development 

 of mycelium (PL I, fig. 2) is possible, but under conditions of free 

 air circulation the surface is usually kept too dry for this to occur, 

 although the interior of large timbers may still retain sufficient 

 moisture for decay to progress within them. 



Temperature. — Wood- destroying fungi can maintain themselves 

 over rather wide ranges of temperature, but have an optimum for 

 most rapid development within comparatively narrow limits. Ac- 

 cording to German investigations Merulius lachrymans (Wulf.) Fr. 

 has an optimum between 65° and 72° F. (18° and 22° C.) ; Gonio- 

 phora cerehella (Pers.) Schrot. { = C. puteana (Schum.) Fr.) be- 

 tween 72° and 79° F. (22° and 26° C), and Lemites sepiaria (Wulf.) 

 Fr. between 82° and 90° F. (28° and 32° C). 



Growth below these points is often considerably retarded, while 

 a rise of 4 to 8 degrees above the optimum often causes total inhibi- 

 tion of growth or even death, as in the case of Merulius lachrymans^ 

 which is very sensitive to temperature changes above the optimum. 



