DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 557 



So long as sufficient moisture is present, these substances enable the 

 wood to retain its original volume, but whenever water is withdrawn 

 the wood becomes traversed by numerous fissures running at right 

 angles to each other, and frequently, it breaks up into regular cubes 

 which readily crumble away, if rubbed, or compressed, and a brown 

 punky substance is the result of the destructive attack of the myceUum. 



When the opportunity is presented for the mycelium to develop 

 vigorously outside the nourishing substratum, it forms especially on the 

 side of the joist or board, which is facing a moister air-still chamber, as 

 under a porch floor, or the interior of some conduit (electric or other- 

 wise), a skin-Hke layer which often attains large proportions. In other 

 cases, it may fill cracks, or other cavities. If a microscopic examina- 

 tion is made of the hyphae of the dry-rot fungus, they will be found of 

 several kinds showing clamp-connections (Schnallenbildungen), the 

 formation of oidia and the anastomosis of hyphae that come in contact. 

 The hyphal cells are multi-nucleate. Three kinds of structural hyphae 

 are discernible, viz., the ordinary thin- walled hyphae, the water-con- 

 ducting hyphae of larger size and thicker walls, and the sclerenchyma- 

 like hyphae with very much thicker walls than the other two. The 

 function of the water-conducting hyphae will be explained, if we examine 

 the sheet-like mycelia, which cover at times the surface of structural 

 wood. Such a mycelium will be found covered with drops of extruded 

 water like tear drops (hence lacrymans > Lat. lacryma, a tear). This 

 water has been conveyed from the soil, or damp wall, in contact with 

 the joist, a beam, a distance sometimes of ten or twelve feet to the 

 drier parts of the wood*. This accounts for the rapid spread of the 

 mycelium and its abiHty to secure enough water for its insidious growth 

 through well-seasoned timbers. Sometimes in houses only a thin coat 

 of paint conceals the destructive work of the "house-fungus." Later the 

 fruit bodies appear as an extended thin superficial crust of a brownish- 

 smoke color covered with low anastomosing ridges and wrinkles, sug- 

 gesting the surface of tripe, over which the hymenial, or basidial, layer 

 is spread (Fig. 89). The basidiospores are deep yellowish-brown in 

 color and impart to the hymenium a yellowish-brown hue. Each 

 basidium terminates in four short sterigma which bear the basidio- 

 spores, which measure g/j. to i2yu in length by 5.5/x to 6.5^t in breadth. 

 Germination of the spores is readily obtained. 



Kiln drying of structural wood is an excellent means of preventing 



