SAP-STAIN, MOLD, AND DECAY IN GREEN WOOD. 15 



amount of moisture ; a temperature range within certain limits ; and 

 the necessary food substances. 



Air. — Fungi require oxygen for their growth. This is supplied as 

 one of the constitutents of ordinary air. Even under storage con- 

 ditions the supply is ample. Stagnant air containing a considerable 

 amount of moisture is favorable to the growth of fungi in the timber, 

 in that it prevents the drying of the wood. Timber entirely sub- 

 merged in water is practically immune from fungous attacks, since 

 the supply of oxygen is cut oif. 



Moisture. — The extent of the growth of sap-stain and mold fungi 

 is largely dependent upon the amount of moisture present in the 

 substratum. This moisture content in green timbers of different 

 species as well as in the sapwood and heartwood of a particular 

 species may vary considerably. Thus, according to Tiemann {51, 

 p. 106; 33, tables), the green sapwood of conifers may contain from 

 100 to 150 per cent moisture,^^ while the heartwood, probably being 

 near its fiber saturation point, contains about 30 per cent. In the case 

 of the hardwoods, both heartwood and sapwood may contain from 

 60 to over 200 per cent moisture. Frequently, however, there is pres- 

 ent a greater quantity of free water in the sapwood than in the heart- 

 wood (Tiemann, 5J). In air-dried timber the amount of moisture 

 may be reduced to anywhere from 8 to 18 per cent, according to the 

 climate. In kiln-dried material it may be reduced to 3 to 15 per 

 cent moisture, depending upon requirement and uses. This will 

 explain why mold and sap-stain, so frequently found in green timber, 

 are absent in thoroughly air-seasoned or kiln-dried stock. Air cur- 

 rents will often surface-dry the timber to an extent that will make 

 it practically impossible for fungi to grow thereon. 



The relative quantities of water and air found in the wood, accord- 

 ing to Von Schrenk (4-3), are the most important factors in the con- 

 trol of the rate of growth and spread of the sap-stain fungus. He 

 cites Miinch's experiments (5^) on artificially inoculated pine blocks,^^ 

 differing only in the relative amounts of contained water and air. 

 These experiments seem to indicate that the growth of the fungus is 

 inhibited when the normal winter water content of the wood is raised 

 to an amount that will insure a consequent reduction in the volume of 

 contained air to at least 15 per cent, based on the volume of the fresh 

 wood. According to Miinch {3£) an air content of 42 per cent, 

 brought about through a reduction of the normal winter water con- 

 tent of the wood, is the optimum for development of the fungus in 

 the wood. Miinch {31, p. 59-62) states that the sap-stain fungus at- 



^^ Unless otherwise stated, all percentages of moisture content are based upon oven- 

 dry weight. 



^- The blocks in this case were artificially inoculated with the conidia of Ccratosto- 

 mella coemlea. 



