TIMBER STOEAGE IN THE EASTERN AND SOUTHERN STATES. 6 
rials readily available to the fungus and whose Avails 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 (-1) 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 this 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, which 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 (PI. 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-destro} 7 ing 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 lachrymam (Wulf.) Fr. 
has an optimum between 65° and 72° F. (18° and 22° C.) ; Conio- 
phora cerebella (Pers.) Schrot. ( = 0. 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. 
