262 INTRODUCTION TO CRYPTOGAJVIIC BOTANY. 



with which they are in contact, and thus in a few hours the 

 whole mass is involved in ruin. 



260. But Fungi are no less destructive to all kinds of 

 wooden fabrics. Our houses and ships are equally the 

 victims of certain species, which live at the expense of the raw 

 matter contained in the woody tissue. Polyporus destructor, 

 Merulius lacrymans, and others, soon establish themselves 

 wherever there is ill-seasoned wood or a close atmosphere, in 

 some cases destroying everything before them in a few years, 

 and sometimes in an incredibly small space of time. Merulius 

 lacrymans sometimes even extends from the woodwork to the 

 walls themselves, and by penetrating their interstices involves 

 them in destruction no less than the wood itself Wood which 

 was perfectly untainted when first placed in the structure is 

 soon attacked, but the evil is often pre-existent. Many of our 

 timber trees are deeply tainted before they are felled ; and oak, 

 where raised from old stools, and not from acorns, is extremely 

 subject to be impaired by the mycelium of Dcedalea quercina. 

 Hothouses, and similar fabrics, made of such materials, soon 

 show indubitable signs of the evil, which in a few years goes 

 through its work of destruction. In all such cases, a free cir- 

 culation of air is indispensable ; but besides this, timber felled 

 in winter and free from raw sap, is far less subject than when 

 spring-felled, though some authorities are against such view. 

 In every case, if there is fear of dry-rot, the timber should be 

 steeped in a solution of corrosive subHmate, sulphate of cop- 

 per, or some other mineral substance, inimical to the growth 

 of Fungi. The large pileate Fungi do not always appear in 

 the most aggravated cases of dry-rot. In some of the worst 

 there are merely imperfect mycelia, under the form of Sporo- 

 trichum ; but these have as destructive powers, penetrate as 

 deeply into the wood, and attract moisture from the air, as 

 effectually as the most perfectly developed species. The won- 

 derfid power of penetration possessed by mycelium, may be 

 easily seen in any dark-coloured Fungus, by making thin 

 vertical sections through the wood. Not only do the threads 

 penetrate between the cells, but into their cavities themselves, 

 at length completely blocking up the aperture, after traversing 



