CAUSES OF DECAY. 



55 



confine themselves to eating up the starch found in the cells, as shown 



in fig. 36, and merely leave a stain (bluing of lumber). In all cases 



of decay we find the vegetative bodies, these slender threads of fungi, 



responsible for the mischief. These fine threads 



are the vegetative body of the fungus, the little 



shelf is its fruiting body, on which it produces 



myriads of little spores (the seeds of fungi). 



Some fungi attack only conifers, others hard 



woods; many are confined to one species of tree 



and perhaps no one attacks all kinds of wood. 



One kind produces "red rot," others "bluing. 1 ' 



In one case the decayed tracts are tubular, 



and in the direction of 

 the fibers the wood is 

 "peggy." In other cases 

 no particular shapes are 

 discernible. 



Cutting off a disk of 

 loblolly pine, washing it, 

 and then laying it in a 

 clean, shady place in the 

 sawmill, its sapwood will 

 be found stained in a few 

 days. Sor is this mis- 

 chief confined to the sur- 

 face ; it penetrates the sapwood of the entire disk. 

 From this it appears that the spores must have 

 been in the air about the mill, and also that their 

 germination and the growth of the threads or 

 mycelium is exceedingly rapid. (Watching the 

 progress of mold on a piece of bread teaches the 

 same thing.) Placing a fresh piece of sapwood 

 on ice, another into a dry kiln, and soaking a few 

 others in solutions of corrosive sublimate (mer- 

 curic chloride) and other similar salts, we learn 

 that the fungus growth is retarded by cold, pre- 

 vented and killed by temperatures over 150° F., 

 and that salts of mercury, etc., have the same 

 effect. The fact that seasoned pieces if exposed 

 are not so readily attacked by fungi shows that 

 the moisture in air-dry wood is insufficient for 

 fungus growth. 



From this it appears that warmth, preferably 



between 60° and 100° F., combined with abundance of moisture (but 



not immersion), is the most important condition favoring decay, and 



that the defense lies in the proper regulation or avoidance of these 



Fig. 34.— "Shelf " fungus on the 

 stem of a pine. (Hartig.) «, 

 sound wood; 6, resinous 

 "light" wood; c, partly de- 

 cayed wood or punk ; d, layer 

 of living spore tubes; e, old 

 filled up spore tubes ; /, fluted 

 upper surface of the fruiting 

 body of the fungus, which 

 gets its food through a great 

 number of fine threads (the 

 mycelium), its vegetative tis- 

 sue penetrating the wood and 

 causing its decay. 



Fig. 35. — Fungus threads in 

 pine wood. (Hartig.) a, 

 cell wall of the wood fibers; 

 b, bordered pits of these 

 fibers; e, thread of myce- 

 lium of the fungus ; d, holes 

 in the cell walls made by 

 the fungus threads, which 

 gradually dissolve the 

 walls as shown at e. and 

 thus break down the wood 

 structure. 



