TREES AND TIMBER 429 



It can be prevented by impregnating the wood with vari- 

 ous antiseptics, as creosote or zinc chloride.^ 



A few of the chief causes of the decay of dead wood are as 

 follows : — 



Polyporose {Polyporus pinicola). See p. 422. 



Dry rot, meruliose {Merulius lacrytnans (Jcq.) Fr.)- — 

 One of the most common and destructive of all the rots 

 of structural timber, this renders the wood spongy and 

 ])rownish. If very moist, a profuse superficial pure white 

 mycehum may develop, at first loosely, later in dense sheets 

 or strands. The sporophores are flat, at first white, later red, 

 and still later yellow-brown. The spore-bearing surface 

 carries shallow pores penned between folds and wrinkles. 



Sap rot (Polystidis versicolor (L.) Fr.) . — In addition to 

 its parasitic life upon the chestnut and catalpa, this fungus 

 grows as a saprophyte upon all kinds of deciduous woods, 

 and is " regarded as the most serious of all wood-rotting 

 fungi which attack the dead wood of broad-leaf trees.^ 

 It destroys probably 75 per cent or more of the broad- 

 leaf species of timber used for tie purposes." "When- 

 ever broad-leaf species of wood are used for fencing for 

 posts or poles, or for any purpose where they come in con- 

 tact with the soil, they are sure to be attacked sooner or 

 later by Polystictis versicolor." 



Polyporose (Polyporus pergamenus Fr .) . — This fungus is 

 similar to Polystictis versicolor, and of great importance, 

 appearing upon cut timber or on large wounded surfaces 



' For details see Sherfesee, W. F., Bui. 78, Forestry Service, November 

 11, 1909. 



2 Von Schrenk, H., and Spaulding, Parley, U.S. Dept. Agr. Bur. Plant 

 Indus. Bui. 149. 



