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). Seep. 422. 



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

 One of the most common and destructive of all the rots 

 of structural timber, this renders the wood spongy and 

 brownish. If very moist, a profuse superficial pure white 

 mycelium 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 {Polystictis 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." 



Pol3rporose {Polyporus pergamenus Ft .) . — 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. 



^ Von Schrenk, H., and Spaulding, Perley, U.S. Dept. Agr. Bur. Plant 

 Indus. Bui. 149. 



